Bash function comment extraction from sourced file - bash

I have a bash script with functions I have sourced from a random file, that I no longer retain the original path.
#!/bin/bash
my_awesome_function()
{
#- Usage: my_awesome_function <key> <to> <success>
echo "I'm doing something great."
}
declare -x -f my_awesome_function
I have previously ran:
$ source ./some_random_file_i_dont_know_where_it_is
And followed up with (in the same shell):
$ type my_awesome_function
my_awesome_function is a function
my_awesome_function ()
{
echo "I'm doing something great."
}
I'm asking because I would like to include automated usage for this function. In the ideal case:
exceptional_help()
{
echo ; type $1 | grep "#-" | tr -d "#-"
}
Which could be used like follows:
$ exceptional_help "my_awesome_function"
Usage: my_awesome_function <key> <to> <success>
I have tried type and declare and which and a few other builtins, but nothing seems to retain the original formatting including comments, or a reference to the original function that I could then parse again.

Try:
my_awesome_function() {
[ "$1" = "--help" ] && {
echo 'Usage: my_awesome_function <key> <to> <success>'
return
}
echo "I'm doing something great."
}
Example:
$ my_awesome_function
I'm doing something great.
$ my_awesome_function --help
Usage: my_awesome_function <key> <to> <success>

In practice, it would be much more reliable to follow #John1024's solution. In its entirety if you can. I wrote a small wrapper around the source functionality that will extract specific comments for docs. That borrows the easy way to write a help string.
For future reference here is a macro orientated approach.
I couldn't quite get sourcing to work from stdin on BSD and bash 4, but I'm sure it is achievable without an intermediary file.
It also did need an additional replacement to close the brackets and this doesn't play nice with multi-line usage strings.
Random file:
my_awesome_function(){
#--Usage : hello <arg1> <arg2> ++#
echo "I'm doing something great."
echo "and I'm totally self documented."
}
Custom sourcing :
self_documenting_source(){
local src tmpfile
src=$1
tmpfile=$(mktemp /tmp/source.XXXXXX)
< $src \
sed 's/#--/[ "$1" == "--help" ] \&\& { echo \" /' \
| sed 's/#++/\"; return; }/' \
> $tmpfile
source $tmpfile
rm $tmpfile
}
(As a side note, turns out the & represents the input substitution in BSD sed.)
Results:
$ my_function --help
Usage : hello <arg1> <arg2>
$ my_function
I'm doing something great.
and I'm totally self documented.

Related

Need help setting up an alias in bash [duplicate]

I used to use CShell (csh), which lets you make an alias that takes a parameter. The notation was something like
alias junk="mv \\!* ~/.Trash"
In Bash, this does not seem to work. Given that Bash has a multitude of useful features, I would assume that this one has been implemented but I am wondering how.
Bash alias does not directly accept parameters. You will have to create a function.
alias does not accept parameters but a function can be called just like an alias. For example:
myfunction() {
#do things with parameters like $1 such as
mv "$1" "$1.bak"
cp "$2" "$1"
}
myfunction old.conf new.conf #calls `myfunction`
By the way, Bash functions defined in your .bashrc and other files are available as commands within your shell. So for instance you can call the earlier function like this
$ myfunction original.conf my.conf
Refining the answer above, you can get 1-line syntax like you can for aliases, which is more convenient for ad-hoc definitions in a shell or .bashrc files:
bash$ myfunction() { mv "$1" "$1.bak" && cp -i "$2" "$1"; }
bash$ myfunction original.conf my.conf
Don't forget the semi-colon before the closing right-bracket. Similarly, for the actual question:
csh% alias junk="mv \\!* ~/.Trash"
bash$ junk() { mv "$#" ~/.Trash/; }
Or:
bash$ junk() { for item in "$#" ; do echo "Trashing: $item" ; mv "$item" ~/.Trash/; done; }
The question is simply asked wrong. You don't make an alias that takes parameters because alias just adds a second name for something that already exists. The functionality the OP wants is the function command to create a new function. You do not need to alias the function as the function already has a name.
I think you want something like this :
function trash() { mv "$#" ~/.Trash; }
That's it! You can use parameters $1, $2, $3, etc, or just stuff them all with $#
TL;DR: Do this instead
Its far easier and more readable to use a function than an alias to put arguments in the middle of a command.
$ wrap_args() { echo "before $# after"; }
$ wrap_args 1 2 3
before 1 2 3 after
If you read on, you'll learn things that you don't need to know about shell argument processing. Knowledge is dangerous. Just get the outcome you want, before the dark side forever controls your destiny.
Clarification
bash aliases do accept arguments, but only at the end:
$ alias speak=echo
$ speak hello world
hello world
Putting arguments into the middle of command via alias is indeed possible but it gets ugly.
Don't try this at home, kiddies!
If you like circumventing limitations and doing what others say is impossible, here's the recipe. Just don't blame me if your hair gets frazzled and your face ends up covered in soot mad-scientist-style.
The workaround is to pass the arguments that alias accepts only at the end to a wrapper that will insert them in the middle and then execute your command.
Solution 1
If you're really against using a function per se, you can use:
$ alias wrap_args='f(){ echo before "$#" after; unset -f f; }; f'
$ wrap_args x y z
before x y z after
You can replace $# with $1 if you only want the first argument.
Explanation 1
This creates a temporary function f, which is passed the arguments (note that f is called at the very end). The unset -f removes the function definition as the alias is executed so it doesn't hang around afterwards.
Solution 2
You can also use a subshell:
$ alias wrap_args='sh -c '\''echo before "$#" after'\'' _'
Explanation 2
The alias builds a command like:
sh -c 'echo before "$#" after' _
Comments:
The placeholder _ is required, but it could be anything. It gets set to sh's $0, and is required so that the first of the user-given arguments don't get consumed. Demonstration:
sh -c 'echo Consumed: "$0" Printing: "$#"' alcohol drunken babble
Consumed: alcohol Printing: drunken babble
The single-quotes inside single-quotes are required. Here's an example of it not working with double quotes:
$ sh -c "echo Consumed: $0 Printing: $#" alcohol drunken babble
Consumed: -bash Printing:
Here the values of the interactive shell's $0 and $# are replaced into the double quoted before it is passed to sh. Here's proof:
echo "Consumed: $0 Printing: $#"
Consumed: -bash Printing:
The single quotes ensure that these variables are not interpreted by interactive shell, and are passed literally to sh -c.
You could use double-quotes and \$#, but best practice is to quote your arguments (as they may contain spaces), and \"\$#\" looks even uglier, but may help you win an obfuscation contest where frazzled hair is a prerequisite for entry.
All you have to do is make a function inside an alias:
$ alias mkcd='_mkcd(){ mkdir "$1"; cd "$1";}; _mkcd'
^ * ^ ^ ^ ^ ^
You must put double quotes around "$1" because single quotes will not work. This is because clashing the quotes at the places marked with arrows confuses the system. Also, a space at the place marked with a star is needed for the function.
Once I did some fun project and I'm still using it. It's showing some animation while copy files via cp command coz cp don't show anything and it's kind of frustrating. So I've made this alias for cp:
alias cp="~/SCR/spinner cp"
And this is the spinner script
#!/bin/bash
#Set timer
T=$(date +%s)
#Add some color
. ~/SCR/color
#Animation sprites
sprite=( "(* ) ( *)" " (* )( *) " " ( *)(* ) " "( *) (* )" "(* ) ( *)" )
#Print empty line and hide cursor
printf "\n${COF}"
#Exit function
function bye { printf "${CON}"; [ -e /proc/$pid ] && kill -9 $pid; exit; }; trap bye INT
#Run our command and get its pid
"$#" & pid=$!
#Waiting animation
i=0; while [ -e /proc/$pid ]; do sleep 0.1
printf "\r${GRN}Please wait... ${YLW}${sprite[$i]}${DEF}"
((i++)); [[ $i = ${#sprite[#]} ]] && i=0
done
#Print time and exit
T=$(($(date +%s)-$T))
printf "\n\nTime taken: $(date -u -d #${T} +'%T')\n"
bye
It looks like this
Cycled animation)
Here is the link to a color script mentioned above.
And new animation cycle)
So the answer to the OP's question is to use intermediate script that could shuffle args as you wish.
An alternative solution is to use marker, a tool I've created recently that allows you to "bookmark" command templates and easily place cursor at command place-holders:
I found that most of time, I'm using shell functions so I don't have to write frequently used commands again and again in the command-line. The issue of using functions for this use case, is adding new terms to my command vocabulary and having to remember what functions parameters refer to in the real-command. Marker goal is to eliminate that mental burden.
Syntax:
alias shortName="your custom command here"
Example:
alias tlogs='_t_logs() { tail -f ../path/$1/to/project/logs.txt ;}; _t_logs'
Bash alias absolutely does accept parameters. I just added an alias to create a new react app which accepts the app name as a parameter. Here's my process:
Open the bash_profile for editing in nano
nano /.bash_profile
Add your aliases, one per line:
alias gita='git add .'
alias gitc='git commit -m "$#"'
alias gitpom='git push origin master'
alias creact='npx create-react-app "$#"'
note: the "$#" accepts parameters passed in like "creact my-new-app"
Save and exit nano editor
ctrl+o to to write (hit enter); ctrl+x to exit
Tell terminal to use the new aliases in .bash_profile
source /.bash_profile
That's it! You can now use your new aliases
Here's are three examples of functions I have in my ~/.bashrc, that are essentially aliases that accept a parameter:
#Utility required by all below functions.
#https://stackoverflow.com/questions/369758/how-to-trim-whitespace-from-bash-variable#comment21953456_3232433
alias trim="sed -e 's/^[[:space:]]*//g' -e 's/[[:space:]]*\$//g'"
.
:<<COMMENT
Alias function for recursive deletion, with are-you-sure prompt.
Example:
srf /home/myusername/django_files/rest_tutorial/rest_venv/
Parameter is required, and must be at least one non-whitespace character.
Short description: Stored in SRF_DESC
With the following setting, this is *not* added to the history:
export HISTIGNORE="*rm -r*:srf *"
- https://superuser.com/questions/232885/can-you-share-wisdom-on-using-histignore-in-bash
See:
- y/n prompt: https://stackoverflow.com/a/3232082/2736496
- Alias w/param: https://stackoverflow.com/a/7131683/2736496
COMMENT
#SRF_DESC: For "aliaf" command (with an 'f'). Must end with a newline.
SRF_DESC="srf [path]: Recursive deletion, with y/n prompt\n"
srf() {
#Exit if no parameter is provided (if it's the empty string)
param=$(echo "$1" | trim)
echo "$param"
if [ -z "$param" ] #http://tldp.org/LDP/abs/html/comparison-ops.html
then
echo "Required parameter missing. Cancelled"; return
fi
#Actual line-breaks required in order to expand the variable.
#- https://stackoverflow.com/a/4296147/2736496
read -r -p "About to
sudo rm -rf \"$param\"
Are you sure? [y/N] " response
response=${response,,} # tolower
if [[ $response =~ ^(yes|y)$ ]]
then
sudo rm -rf "$param"
else
echo "Cancelled."
fi
}
.
:<<COMMENT
Delete item from history based on its line number. No prompt.
Short description: Stored in HX_DESC
Examples
hx 112
hx 3
See:
- https://unix.stackexchange.com/questions/57924/how-to-delete-commands-in-history-matching-a-given-string
COMMENT
#HX_DESC: For "aliaf" command (with an 'f'). Must end with a newline.
HX_DESC="hx [linenum]: Delete history item at line number\n"
hx() {
history -d "$1"
}
.
:<<COMMENT
Deletes all lines from the history that match a search string, with a
prompt. The history file is then reloaded into memory.
Short description: Stored in HXF_DESC
Examples
hxf "rm -rf"
hxf ^source
Parameter is required, and must be at least one non-whitespace character.
With the following setting, this is *not* added to the history:
export HISTIGNORE="*hxf *"
- https://superuser.com/questions/232885/can-you-share-wisdom-on-using-histignore-in-bash
See:
- https://unix.stackexchange.com/questions/57924/how-to-delete-commands-in-history-matching-a-given-string
COMMENT
#HXF_DESC: For "aliaf" command (with an 'f'). Must end with a newline.
HXF_DESC="hxf [searchterm]: Delete all history items matching search term, with y/n prompt\n"
hxf() {
#Exit if no parameter is provided (if it's the empty string)
param=$(echo "$1" | trim)
echo "$param"
if [ -z "$param" ] #http://tldp.org/LDP/abs/html/comparison-ops.html
then
echo "Required parameter missing. Cancelled"; return
fi
read -r -p "About to delete all items from history that match \"$param\". Are you sure? [y/N] " response
response=${response,,} # tolower
if [[ $response =~ ^(yes|y)$ ]]
then
#Delete all matched items from the file, and duplicate it to a temp
#location.
grep -v "$param" "$HISTFILE" > /tmp/history
#Clear all items in the current sessions history (in memory). This
#empties out $HISTFILE.
history -c
#Overwrite the actual history file with the temp one.
mv /tmp/history "$HISTFILE"
#Now reload it.
history -r "$HISTFILE" #Alternative: exec bash
else
echo "Cancelled."
fi
}
References:
Trimming whitespace from strings: How to trim whitespace from a Bash variable?
Actual line breaks: https://stackoverflow.com/a/4296147/2736496
Alias w/param: https://stackoverflow.com/a/7131683/2736496 (another answer in this question)
HISTIGNORE: https://superuser.com/questions/232885/can-you-share-wisdom-on-using-histignore-in-bash
Y/N prompt: https://stackoverflow.com/a/3232082/2736496
Delete all matching items from history: https://unix.stackexchange.com/questions/57924/how-to-delete-commands-in-history-matching-a-given-string
Is string null/empty: http://tldp.org/LDP/abs/html/comparison-ops.html
Respectfully to all those saying you can't insert a parameter in the middle of an alias I just tested it and found that it did work.
alias mycommand = "python3 "$1" script.py --folderoutput RESULTS/"
when I then ran mycommand foobar it worked exactly as if I had typed the command out longhand.
NB: In case the idea isn't obvious, it is a bad idea to use aliases for anything but aliases, the first one being the 'function in an alias' and the second one being the 'hard to read redirect/source'. Also, there are flaws (which i thought would be obvious, but just in case you are confused: I do not mean them to actually be used... anywhere!)
I've answered this before, and it has always been like this in the past:
alias foo='__foo() { unset -f $0; echo "arg1 for foo=$1"; }; __foo()'
which is fine and good, unless you are avoiding the use of functions all together. in which case you can take advantage of bash's vast ability to redirect text:
alias bar='cat <<< '\''echo arg1 for bar=$1'\'' | source /dev/stdin'
They are both about the same length give or take a few characters.
The real kicker is the time difference, the top being the 'function method' and the bottom being the 'redirect-source' method. To prove this theory, the timing speaks for itself:
arg1 for foo=FOOVALUE
real 0m0.011s user 0m0.004s sys 0m0.008s # <--time spent in foo
real 0m0.000s user 0m0.000s sys 0m0.000s # <--time spent in bar
arg1 for bar=BARVALUE
ubuntu#localhost /usr/bin# time foo FOOVALUE; time bar BARVALUE
arg1 for foo=FOOVALUE
real 0m0.010s user 0m0.004s sys 0m0.004s
real 0m0.000s user 0m0.000s sys 0m0.000s
arg1 for bar=BARVALUE
ubuntu#localhost /usr/bin# time foo FOOVALUE; time bar BARVALUE
arg1 for foo=FOOVALUE
real 0m0.011s user 0m0.000s sys 0m0.012s
real 0m0.000s user 0m0.000s sys 0m0.000s
arg1 for bar=BARVALUE
ubuntu#localhost /usr/bin# time foo FOOVALUE; time bar BARVALUE
arg1 for foo=FOOVALUE
real 0m0.012s user 0m0.004s sys 0m0.004s
real 0m0.000s user 0m0.000s sys 0m0.000s
arg1 for bar=BARVALUE
ubuntu#localhost /usr/bin# time foo FOOVALUE; time bar BARVALUE
arg1 for foo=FOOVALUE
real 0m0.010s user 0m0.008s sys 0m0.004s
real 0m0.000s user 0m0.000s sys 0m0.000s
arg1 for bar=BARVALUE
This is the bottom part of about 200 results, done at random intervals. It seems that function creation/destruction takes more time than redirection. Hopefully this will help future visitors to this question (didn't want to keep it to myself).
If you're looking for a generic way to apply all params to a function, not just one or two or some other hardcoded amount, you can do that this way:
#!/usr/bin/env bash
# you would want to `source` this file, maybe in your .bash_profile?
function runjar_fn(){
java -jar myjar.jar "$#";
}
alias runjar=runjar_fn;
So in the example above, i pass all parameters from when i run runjar to the alias.
For example, if i did runjar hi there it would end up actually running java -jar myjar.jar hi there. If i did runjar one two three it would run java -jar myjar.jar one two three.
I like this $# - based solution because it works with any number of params.
There are legitimate technical reasons to want a generalized solution to the problem of bash alias not having a mechanism to take a reposition arbitrary arguments. One reason is if the command you wish to execute would be adversely affected by the changes to the environment that result from executing a function. In all other cases, functions should be used.
What recently compelled me to attempt a solution to this is that I wanted to create some abbreviated commands for printing the definitions of variables and functions. So I wrote some functions for that purpose. However, there are certain variables which are (or may be) changed by a function call itself. Among them are:
FUNCNAME
BASH_SOURCE
BASH_LINENO
BASH_ARGC
BASH_ARGV
The basic command I had been using (in a function) to print variable defns. in the form output by the set command was:
sv () { set | grep --color=never -- "^$1=.*"; }
E.g.:
> V=voodoo
sv V
V=voodoo
Problem: This won't print the definitions of the variables mentioned above as they are in the current context, e.g., if in an interactive shell prompt (or not in any function calls), FUNCNAME isn't defined. But my function tells me the wrong information:
> sv FUNCNAME
FUNCNAME=([0]="sv")
One solution I came up with has been mentioned by others in other posts on this topic. For this specific command to print variable defns., and which requires only one argument, I did this:
alias asv='(grep -- "^$(cat -)=.*" <(set)) <<<'
Which gives the correct output (none), and result status (false):
> asv FUNCNAME
> echo $?
1
However, I still felt compelled to find a solution that works for arbitrary numbers of arguments.
A General Solution To Passing Arbitrary Arguments To A Bash Aliased Command:
# (I put this code in a file "alias-arg.sh"):
# cmd [arg1 ...] – an experimental command that optionally takes args,
# which are printed as "cmd(arg1 ...)"
#
# Also sets global variable "CMD_DONE" to "true".
#
cmd () { echo "cmd($#)"; declare -g CMD_DONE=true; }
# Now set up an alias "ac2" that passes to cmd two arguments placed
# after the alias, but passes them to cmd with their order reversed:
#
# ac2 cmd_arg2 cmd_arg1 – calls "cmd" as: "cmd cmd_arg1 cmd_arg2"
#
alias ac2='
# Set up cmd to be execed after f() finishes:
#
trap '\''cmd "${CMD_ARGV[1]}" "${CMD_ARGV[0]}"'\'' SIGUSR1;
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# (^This is the actually execed command^)
#
# f [arg0 arg1 ...] – acquires args and sets up trap to run cmd:
f () {
declare -ag CMD_ARGV=("$#"); # array to give args to cmd
kill -SIGUSR1 $$; # this causes cmd to be run
trap SIGUSR1; # unset the trap for SIGUSR1
unset CMD_ARGV; # clean up env...
unset f; # incl. this function!
};
f' # Finally, exec f, which will receive the args following "ac2".
E.g.:
> . alias-arg.sh
> ac2 one two
cmd(two one)
>
> # Check to see that command run via trap affects this environment:
> asv CMD_DONE
CMD_DONE=true
A nice thing about this solution is that all the special tricks used to handle positional parameters (arguments) to commands will work when composing the trapped command. The only difference is that array syntax must be used.
E.g.,
If you want "$#", use "${CMD_ARGV[#]}".
If you want "$#", use "${#CMD_ARGV[#]}".
Etc.
I will just post my (hopefully, okay) solution
(for future readers, & most vitally; editors).
So - please edit & improve/remove anything in this post.
In the terminal:
$ alias <name_of_your_alias>_$argname="<command> $argname"
and to use it (notice the space after '_':
$<name_of_your_alias>_ $argname
for example, a alias to cat a file called hello.txt:
(alias name is CAT_FILE_)
and the $f (is the $argname, which is a file in this example)
$ alias CAT_FILE_$f="cat $f"
$ echo " " >> hello.txt
$ echo "hello there!" >> hello.txt
$ echo " " >> hello.txt
$ cat hello.txt
hello there!
Test (notice the space after '_'):
CAT_FILE_ hello.txt
As has already been pointed out by others, using a function should be considered best practice.
However, here is another approach, leveraging xargs:
alias junk="xargs -I "{}" -- mv "{}" "~/.Trash" <<< "
Note that this has side effects regarding redirection of streams.
Solution with subcommands:
d () {
if [ $# -eq 0 ] ; then
docker
return 0
fi
CMD=$1
shift
case $CMD in
p)
docker ps --all $#
;;
r)
docker run --interactive --tty $#
;;
rma)
docker container prune
docker image prune --filter "dangling=true"
;;
*)
docker $CMD $#
;;
esac
return $?
}
Using:
$ d r my_image ...
Called:
docker run --interactive --tty my_image ...
Here's the example:
alias gcommit='function _f() { git add -A; git commit -m "$1"; } ; _f'
Very important:
There is a space after { and before }.
There is a ; after each command in sequence. If you forget this after the last command, you will see > prompt instead!
The argument is enclosed in quotes as "$1"
To give specific answer to the Question posed about creating the alias to move the files to Trash folder instead of deleting them:
alias rm="mv "$1" -t ~/.Trash/"
Offcourse you have to create dir ~/.Trash first.
Then just give following command:
$rm <filename>
$rm <dirname>
Here is another approach using read. I am using this for brute search of a file by its name fragment, ignoring the "permission denied" messages.
alias loc0='( IFS= read -r x; find . -iname "*" -print 2>/dev/null | grep $x;) <<<'
A simple example:
$ ( IFS= read -r x; echo "1 $x 2 ";) <<< "a b"
1 a b 2
Note, that this converts the argument as a string into variable(s). One could use several parameters within quotes for this, space separated:
$ ( read -r x0 x1; echo "1 ${x0} 2 ${x1} 3 ";) <<< "a b"
1 a 2 b 3
Functions are indeed almost always the answer as already amply contributed and confirmed by this quote from the man page: "For almost every purpose, aliases are superseded by shell functions."
For completeness and because this can be useful (marginally more lightweight syntax) it could be noted that when the parameter(s) follow the alias, they can still be used (although this wouldn't address the OP's requirement). This is probably easiest to demonstrate with an example:
alias ssh_disc='ssh -O stop'
allows me to type smth like ssh_disc myhost, which gets expanded as expected as: ssh -O stop myhost
This can be useful for commands which take complex arguments (my memory isn't what it use t be anymore...)
For taking parameters, you should use functions!
However $# get interpreted when creating the alias instead of during the execution of the alias and escaping the $ doesn’t work either. How do I solve this problem?
You need to use shell function instead of an alias to get rid of this problem. You can define foo as follows:
function foo() { /path/to/command "$#" ;}
OR
foo() { /path/to/command "$#" ;}
Finally, call your foo() using the following syntax:
foo arg1 arg2 argN
Make sure you add your foo() to ~/.bash_profile or ~/.zshrc file.
In your case, this will work
function trash() { mv $# ~/.Trash; }
Both functions and aliases can use parameters as others have shown here. Additionally, I would like to point out a couple of other aspects:
1. function runs in its own scope, alias shares scope
It may be useful to know this difference in cases you need to hide or expose something. It also suggests that a function is the better choice for encapsulation.
function tfunc(){
GlobalFromFunc="Global From Func" # Function set global variable by default
local FromFunc="onetwothree from func" # Set a local variable
}
alias talias='local LocalFromAlias="Local from Alias"; GlobalFromAlias="Global From Alias" # Cant hide a variable with local here '
# Test variables set by tfunc
tfunc # call tfunc
echo $GlobalFromFunc # This is visible
echo $LocalFromFunc # This is not visible
# Test variables set by talias
# call talias
talias
echo $GlobalFromAlias # This is invisible
echo $LocalFromAlias # This variable is unset and unusable
Output:
bash-3.2$ # Test variables set by tfunc
bash-3.2$ tfunc # call tfunc
bash-3.2$ echo $GlobalFromFunc # This is visible
Global From Func
bash-3.2$ echo $LocalFromFunc # This is not visible
bash-3.2$ # Test variables set by talias
bash-3.2$ # call talias
bash-3.2$ talias
bash: local: can only be used in a function
bash-3.2$ echo $GlobalFromAlias # This is invisible
Global From Alias
bash-3.2$ echo $LocalFromAlias # This variable is unset and unusable
2. wrapper script is a better choice
It has happened to me several times that an alias or function can not be found when logging in via ssh or involving switching usernames or multi-user environment. There are tips and tricks with sourcing dot files, or this interesting one with alias: alias sd='sudo ' lets this subsequent alias alias install='sd apt-get install' work as expect (notice the extra space in sd='sudo '). However, a wrapper script works better than a function or alias in cases like this. The main advantage with a wrapper script is that it is visible/executable for under intended path (i.e. /usr/loca/bin/) where as a function/alias needs to be sourced before it is usable. For example, you put a function in a ~/.bash_profile or ~/.bashrc for bash, but later switch to another shell (i.e. zsh) then the function is not visible anymore.
So, when you are in doubt, a wrapper script is always the most reliable and portable solution.
alias junk="delay-arguments mv _ ~/.Trash"
delay-arguments script:
#!/bin/bash
# Example:
# > delay-arguments echo 1 _ 3 4 2
# 1 2 3 4
# > delay-arguments echo "| o n e" _ "| t h r e e" "| f o u r" "| t w o"
# | o n e | t w o | t h r e e | f o u r
RAW_ARGS=("$#")
ARGS=()
ARG_DELAY_MARKER="_"
SKIPPED_ARGS=0
SKIPPED_ARG_NUM=0
RAW_ARGS_COUNT="$#"
for ARG in "$#"; do
#echo $ARG
if [[ "$ARG" == "$ARG_DELAY_MARKER" ]]; then
SKIPPED_ARGS=$((SKIPPED_ARGS+1))
fi
done
for ((I=0; I<$RAW_ARGS_COUNT-$SKIPPED_ARGS; I++)); do
ARG="${RAW_ARGS[$I]}"
if [[ "$ARG" == "$ARG_DELAY_MARKER" ]]; then
MOVE_SOURCE_ARG_NUM=$(($RAW_ARGS_COUNT-$SKIPPED_ARGS+$SKIPPED_ARG_NUM))
MOVING_ARG="${RAW_ARGS[$MOVE_SOURCE_ARG_NUM]}"
if [[ "$MOVING_ARG" == "$ARG_DELAY_MARKER" ]]; then
echo "Error: Not enough arguments!"
exit 1;
fi
#echo "Moving arg: $MOVING_ARG"
ARGS+=("$MOVING_ARG")
SKIPPED_ARG_NUM=$(($SKIPPED_ARG_NUM+1))
else
ARGS+=("$ARG")
fi
done
#for ARG in "${ARGS[#]}"; do
#echo "ARGN: $ARG"
#done
#echo "RAW_ARGS_COUNT: $RAW_ARGS_COUNT"
#echo "SKIPPED_ARGS: $SKIPPED_ARGS"
#echo "${ARGS[#]}"
QUOTED_ARGS=$(printf ' %q' "${ARGS[#]}")
eval "${QUOTED_ARGS[#]}"

Is there a Bash wrapper (program/script) that enables a more succinct input when I want multiple outputs in one Bash call

I'm currently creating monstrosities like the following:
ll /home && echo -e "==============\n" && getent passwd && echo -e "==============\n" && ll /opt/tomcat/ && echo -e "==============\n" && ll /etc/sudoers.d/
Is there perhaps some program that handles this in a nicer way?
Something like this (the hypothetical name of the program would be multiprint in my example):
multiprint --delim-escapechars true --delim "============\n" '{ll /home},{getent passwd},...'
alternatively:
multiprint -de "============\n" '{ll /home},{getent passwd},...'
A function like the following would give you that ability :
function intersect() {
delim=$1
shift
for f; do cat "$f"; echo "$delim"; done
}
You could call it as follows to implement your specific use-case :
intersect '==============' <(ll /home) <(getent passwd) <(ll /opt/tomcat/) <(ll /etc/sudoers.d/)
You can try it here.
printf will repeat its format until its arguments are exhausted. You could write something like
printf '%s\n================\n' "$(ll /home)" "$(getent passed)" "$(ll /opt/tomcat)" "$(ll /etc/sudoers.d)"
although this is a little memory-intensive, since it buffers all the output in memory until all the commands have completed.
Based on #Aaron's answer I ended up creating this multiprint.sh Bash shell script, and for what it's worth posting it here:
#!/bin/bash
# Print output of multiple commands, delimited by a specified string
function multiprint() {
if [[ -z "$*" ]]; then
__multiprint_usage
return 0
elif [[ "$1" == "--help" ]]; then
__multiprint_usage
return 0
else
delim=$1
shift
for f; do cat "$f"; echo -e "$delim"; done
fi
}
function __multiprint_usage() {
echo "Usage:"
echo " multiprint '<delimiter>' <(cmd1) <(cmd2) ..."
# example: multiprint '\n\n\n' <(ll /home/) <(ll /var/) ..."
}

How to make a bash function which can read from standard input?

I have some scripts that work with parameters, they work just fine but i would like them to be able to read from stdin, from a pipe for example, an example, suppose this is called read:
#!/bin/bash
function read()
{
echo $*
}
read $*
Now this works with read "foo" "bar", but I would like to use it as:
echo "foo" | read
How do I accomplish this?
It's a little tricky to write a function which can read standard input, but works properly when no standard input is given. If you simply try to read from standard input, it will block until it receives any, much like if you simply type cat at the prompt.
In bash 4, you can work around this by using the -t option to read with an argument of 0. It succeeds if there is any input available, but does not consume any of it; otherwise, it fails.
Here's a simple function that works like cat if it has anything from standard input, and echo otherwise.
catecho () {
if read -t 0; then
cat
else
echo "$*"
fi
}
$ catecho command line arguments
command line arguments
$ echo "foo bar" | catecho
foo bar
This makes standard input take precedence over command-line arguments, i.e., echo foo | catecho bar would output foo. To make arguments take precedence over standard input (echo foo | catecho bar outputs bar), you can use the simpler function
catecho () {
if [ $# -eq 0 ]; then
cat
else
echo "$*"
fi
}
(which also has the advantage of working with any POSIX-compatible shell, not just certain versions of bash).
You can use <<< to get this behaviour. read <<< echo "text" should make it.
Test with readly (I prefer not using reserved words):
function readly()
{
echo $*
echo "this was a test"
}
$ readly <<< echo "hello"
hello
this was a test
With pipes, based on this answer to "Bash script, read values from stdin pipe":
$ echo "hello bye" | { read a; echo $a; echo "this was a test"; }
hello bye
this was a test
To combine a number of other answers into what worked for me (this contrived example turns lowercase input to uppercase):
uppercase() {
local COMMAND='tr [:lower:] [:upper:]'
if [ -t 0 ]; then
if [ $# -gt 0 ]; then
echo "$*" | ${COMMAND}
fi
else
cat - | ${COMMAND}
fi
}
Some examples (the first has no input, and therefore no output):
:; uppercase
:; uppercase test
TEST
:; echo test | uppercase
TEST
:; uppercase <<< test
TEST
:; uppercase < <(echo test)
TEST
Step by step:
test if file descriptor 0 (/dev/stdin) was opened by a terminal
if [ -t 0 ]; then
tests for CLI invocation arguments
if [ $# -gt 0 ]; then
echo all CLI arguments to command
echo "$*" | ${COMMAND}
else if stdin is piped (i.e. not terminal input), output stdin to command (cat - and cat are shorthand for cat /dev/stdin)
else
cat - | ${COMMAND}
Here is example implementation of sprintf function in bash which uses printf and standard input:
sprintf() { local stdin; read -d '' -u 0 stdin; printf "$#" "$stdin"; }
Example usage:
$ echo bar | sprintf "foo %s"
foo bar
This would give you an idea how function can read from standard input.
Late to the party here. Building off of #andy's answer, here's how I define my to_uppercase function.
if stdin is not empty, use stdin
if stdin is empty, use args
if args are empty, do nothing
to_uppercase() {
local input="$([[ -p /dev/stdin ]] && cat - || echo "$#")"
[[ -n "$input" ]] && echo "$input" | tr '[:lower:]' '[:upper:]'
}
Usages:
$ to_uppercase
$ to_uppercase abc
ABC
$ echo abc | to_uppercase
ABC
$ to_uppercase <<< echo abc
ABC
Bash version info:
$ bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin17)
I've discovered that this can be done in one line using test and awk...
test -p /dev/stdin && awk '{print}' /dev/stdin
The test -p tests for input on a pipe, which accepts input via stdin. Only if input is present do we want to run the awk since otherwise it will hang indefinitely waiting for input which will never come.
I've put this into a function to make it easy to use...
inputStdin () {
test -p /dev/stdin && awk '{print}' /dev/stdin && return 0
### accepts input if any but does not hang waiting for input
#
return 1
}
Usage...
_stdin="$(inputStdin)"
Another function uses awk without the test to wait for commandline input...
inputCli () {
local _input=""
local _prompt="$1"
#
[[ "$_prompt" ]] && { printf "%s" "$_prompt" > /dev/tty; }
### no prompt at all if none supplied
#
_input="$(awk 'BEGIN {getline INPUT < "/dev/tty"; print INPUT}')"
### accept input (used in place of 'read')
### put in a BEGIN section so will only accept 1 line and exit on ENTER
### WAITS INDEFINITELY FOR INPUT
#
[[ "$_input" ]] && { printf "%s" "$_input"; return 0; }
#
return 1
}
Usage...
_userinput="$(inputCli "Prompt string: ")"
Note that the > /dev/tty on the first printf seems to be necessary to get the prompt to print when the function is called in a Command Substituion $(...).
This use of awk allows the elimination of the quirky read command for collecting input from keyboard or stdin.
Yet another version that:
works by passing text through a pipe or from arguments
easy to copy and paste by changing command in last line
works in bash, zsh
# Prints a text in a decorated ballon
function balloon()
{
(test -p /dev/stdin && cat - || echo $#) figlet -t | cowsay -n -f eyes | toilet -t --gay -f term
}
Usage:
# Using with a pipe
$ fortune -s | balloon
# Passing text as parameter
balloon "$(fortune -s )"

How to export an associative array (hash) in bash?

Related, but not a duplicate of: How to define hash tables in Bash?
I can define and use a bash hash, but I am unable to export it, even with the -x flag. For example, the following works to export (and test exportation of) a normal string variable:
aschirma#graphics9-lnx:/$ export animal_cow="moo"
aschirma#graphics9-lnx:/$ bash -c "echo \$animal_cow"
moo
aschirma#graphics9-lnx:/$
However, if I try to export a hash:
aschirma#graphics9-lnx:/$ declare -A -x animals
aschirma#graphics9-lnx:/$ animals[duck]="quack"
aschirma#graphics9-lnx:/$ echo ${animals[duck]}
quack
aschirma#graphics9-lnx:/$ bash -c "echo \${animals[duck]}"
aschirma#graphics9-lnx:/$
It seems the nested bash shell does not have the hash in its scope. I did verify this also by manually entering the nested bash shell and attempting to use the hash interactively.
There isn't really a good way to encode an array variable into the environment. See
http://www.mail-archive.com/bug-bash#gnu.org/msg01774.html (Chet Ramey is the maintainer of bash)
As a workaround for this harsh Bash limitation I'm using "serialize to temporary file" method. You can export plain variables, so you can pass an array (associative) through filepath. Of course, this has limitations, but sometimes works and is good enough.
declare -A MAP # export associative array
MAP[bar]="baz"
declare -x serialized_array=$(mktemp) # create temporary variable
# declare -p can be used to dump the definition
# of a variable as shell code ready to be interpreted
declare -p MAP > "${serialized_array}" # serialize an array in temporary file
# perform cleanup after finishing script
cleanup() {
rm "${serialized_array}"
}
trap cleanup EXIT
# ... in place where you need this variable ...
source "${serialized_array}" # deserialize an array
echo "map: ${MAP[#]}"
This is a bit old but I answer anyway, you could use temp files. If you do it right you can wrapper it to use them like arrays. For example with this function:
var() { # set var or add comtent
case $1 in
*=|*=*)
local __var_part1=$( echo "$1" | sed -e 's/=.*//' -e 's/[+,-]//' ) # cut +=/=
local __var_part2=$( echo "$1" | sed -e 's/.*.=//' )
local __var12=$tmp_dir/$__var_part1
mkdir -p ${__var12%/*} #create all subdirs if its an array
case $1 in
*+=*)
# if its an array try to add new item
if [ -d $tmp_dir/$__var_part1 ] ; then
printf -- $__var_part2 > $tmp_dir/$__var_part1/\ $((
$( echo $tmp_dir/$__var_part2/* \
| tail | basename )\ + 1 ))
else
printf -- "$__var_part2" >> $tmp_dir/$__var_part1
fi
;;
*-=*) false ;;
# else just add content
*) printf -- "$__var_part2" > $tmp_dir/$__var_part1 ;;
esac
;;
*) # just print var
if [ -d $tmp_dir/$1 ] ; then
ls $tmp_dir/$1
elif [ -e $tmp_dir/$1 ] ; then
cat $tmp_dir/$1
else
return 1
fi
;;
esac
}
# you can use mostly like you set vars in bash/shell
var test='Hello Welt!'
# if you need arrays set it like this:
var fruits/0='Apple'
var fruits/1='Banana'
# or if you need a dict:
var contacts/1/name="Max"
var contacts/1/surname="Musterman"
This not the fastest way, but its very flexible, simple and works in nearly all shells.
short answer --> export animals after declaring it
full -->
Try this way as a script:
#!/usr/bin/env bash
declare -A -x animals
export animals
animals[duck]="quack"
echo ${animals[duck]}
bash -c "echo ${animals[duck]}"
Output on my side using Bash version: 5.1.16(1)
quack
quack
or in terminal:
$ declare -A -x animals
$ export animals
$ animals[duck]="quack"
$ echo ${animals[duck]}
quack
$ bash -c "echo ${animals[duck]}"
quack
$

Generate warning when multiple executables in path when executing command in bash

Say I have:
>which -a foo
/bin/foo
/usr/bin/foo
I want something like:
>foo
Warning: multiple foo in PATH
... foo gets executed ...
This functionality would have saved me really really lots of time today.
I should have guessed this is happening earlier but the problem was unclear
to me at the beggining and I started to dig in quite opposite direction.
Well, you can do it, but it is not so easy as you may think.
First, you need to create a function that will check
all directories in the PATH, and look there for the command you try to run.
Then you need to bind this function to the DEBUG trap of your current shell.
I wrote a small script that does that:
$ cat /tmp/1.sh
check_command()
{
n=0
DIRS=""
for i in $(echo $PATH| tr : " ")
do
if [ -x "$i/$1" ]
then
n=$[n+1]
DIRS="$DIRS $i"
fi
done
if [ "$n" -gt 1 ]
then
echo "Warning: there are multiple commands in different PATH directories: "$DIRS
fi
}
preexec () {
check_command $1
}
preexec_invoke_exec () {
[ -n "$COMP_LINE" ] && return # do nothing if completing
local this_command=`history 1 | sed -e "s/^[ ]*[0-9]*[ ]*//g"`;
preexec "$this_command"
}
trap 'preexec_invoke_exec' DEBUG
Example of usage:
$ . /tmp/1.sh
$ sudo cp /bin/date /usr/bin/test_it
$ sudo cp /bin/date /bin/test_it
$ test_it
Warning: there are multiple commands in different PATH directories: /usr/bin /bin
Wed Jul 11 15:14:43 CEST 2012
$
It is possible, though a bit trick to generalise. See my answer to https://unix.stackexchange.com/q/42579/20437 for the history and PROMPT_COMMAND magic. Your checkSanity function would look something like this:
checkSanity() {
cmd="${1%% *}" # strip everything but the first word
candidates=$(which -a $cmd | wc -l)
if (( candidates > 1 )); then
echo "Warning: multiple $cmd in PATH"
fi
}
But that will print the warning after the command finishes, not at the start. Use the DEBUG trap instead to get the wanted result:
trap 'checkSanity "$BASH_COMMAND"' DEBUG

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