How to make all user input on command line as stdin for a program?
In my case, I want to replace certain words inputed by user. For example, every time user uses the word animal1, I want it received as goldfish. So it would look like this:
$ animal1
goldfish: command not found
I tried the following bash command
while read input
do
sed "s/animal2/zebra/g;s/animal1/goldfish/g" <<< "$input"
done
But it prompts for user input and does not return to bash. I want it to run while using bash command line.
Also, this allowed me to capture output only.
bash | sed 's/animal2/zebra/g;s/animal1/goldfish/g'
But not user input.
If I understand you correctly, sounds like you just need to set up some aliases:
$ alias animal1=goldfish
$ animal1
bash: goldfish: command not found
This allows the shell to be used interactively as usual but will make the substitutions you want.
You can add this alias definition to one of your startup files, commonly ~/.bashrc or ~/.profile, to have them take effect on any new shell that you open.
The solution provided by Tom Fenech is good, however, if you plan to add more features to the command you can use a function like the following:
animal1() {
echo "Welcome to the new user interface!"
goldfish
# other commands
}
and put it in the user ~/.bashrc or ~/.bash_profile
The output will be:
$>animal1
Welcome to the new user interface!
-bash: goldfish: command not found
By using this approach you can, for example, create a custom output message. In the following snippet I take the return vale from the command and process it word by word. Then I remove the -bash: part of the output and reconstruct the message and output it.
animal1() {
echo "Welcome to the new user interface!"
retval=$(goldfish 2>&1)
# Now retval stores the output of the command glodfish (both stdout and stderr)
# we can give it directly to the user
echo "Default return value"
echo "$retval"
echo
# or test the return value to do something
# here I build a custom message by removing the bash part
message=""
read -ra flds <<< "$retval"
for word in "${flds[#]}" #extract substring from the line
do
# remove bash
msg="$(echo "$word" | grep -v bash)"
# append each word to message
[[ msg ]] && message="$message $msg"
done
echo "Custom message"
echo "$message"
echo
}
Now the output would:
Welcome to the new user interface!
Default return value
-bash: goldfish: command not found
Custom message
goldfish: command not found
If you comment the lines that echoes the default return value then you get exactly the output you asked for.
Related
Here's my problem, from console if I type the below,
var=`history 1`
echo $var
I get the desired output. But when I do the same inside a shell script, it is not showing any output. Also, for other commands like pwd, ls etc, the script shows the desired output without any issue.
As value of variable contains space, add quotes around it.
E.g.:
var='history 1'
echo $var
I believe all you need is this as follows:
1- Ask user for the number till which user need to print the history in script.
2- Run the script and take Input from user and get the output as follows:
cat get_history.ksh
echo "Enter the line number of history which you want to get.."
read number
if [[ $# -eq 0 ]]
then
echo "Usage of script: get_history.ksh number_of_lines"
exit
else
history "$number"
fi
Added logic where it will check arguments if number of arguments passed is 0 then it will exit from script then.
By default history is turned off in a script, therefore you need to turn it on:
set -o history
var=$(history 1)
echo "$var"
Note the preferred use of $( ) rather than the deprecated backticks.
However, this will only look at the history of the current process, that is this shell script, so it is fairly useless.
I need to read command line arguments. First arg is script name. second one is redirection operator i.e. "<" and third one is input filename. When I tried to use "$#", I got 0. When I used "$*", it gave me nothing. I have to use "<" this operator. My input file consists of all user input data. If I don't use the operator, It asks user for the input. Can someone please help me? Thank you !
Command Line :
./script_name < input_file
Script:
echo "$*" # gave nothing
echo "$#" # gave me 0
I need to read input filename and store it to some variable. Then I have to change the extension of it. Any help/suggestions should be appreciated.
When a user runs:
./script_name <input_file
...that's exactly equivalent to if they did the following:
(exec <input_file; exec ./script_name)
...first redirecting stdin from input_file, then invoking the script named ./script_name without any arguments.
There are operating-system-specific interfaces you can use to get the filename associated with a handle (when it has one), but to use one of these would make your script only able to run on an operating system providing that interface; it's not worth it.
# very, very linux-specific, won't work for "cat foo | ./yourscript", generally evil
if filename=$(readlink /proc/self/fd/0) && [[ -e $filename ]]; then
set -- "$#" "$filename" # append filename to the end of the argument list
fi
If you want to avoid prompting for input when an argument is given, and to have the filename of that argument, then don't take it on stdin but as an argument, and do the redirection yourself within the script:
#!/bin/bash
if [[ $1 ]]; then
exec <"$1" # this redirects your stdin to come from the file
fi
# ...put other logic here...
...and have users invoke your script as:
./script_name input_file
Just as ./yourscript <filename runs yourscript with the contents of filename on its standard input, a script invoked with ./yourscript filename which invokes exec <"$1" will have the contents of filename on its stdin after executing that command.
< is used for input redirection. And whatever is at the right side of < is NOT a command line argument.
So, when you do ./script_name < input_file , there will be zero (0) command line arguments passed to the script, hence $# will be zero.
For your puprpose you need to call your script as:
./script_name input_file
And in your script you can change the extension with something like:
mv -- "$1" "${1}_new_extension"
Edit: This was not what OP wanted to do.
Altough, there is already another spot on answer, I will write this for the sake of completeness. If you have to use the '<' redirection you can do something like this in your script.
while read filename; do
mv -- "$filename" "${filename}_bak"
done
And call the script as, ./script < input_file. However, note that you will not be able to take inputs from stdin in this case.
Unfortunately, if you're hoping to take redirection operators as arguments to your script, you're not going to be able to do that without surrounding your command line arguments in quotes:
./script_name "<input_file"
The reason for this is that the shell (at least bash or zsh) processes the command before ever invoking your script. When the shell interprets your command, it reads:
[shell command (./script_name)][shell input redirection (<input_file)]
invoking your script with quotes effectively results in:
[shell command (./script_name)][script argument ("<input_file")]
Sorry this is a few years late; hopefully someone will find this useful.
I often perform configuration changes using single line commands on Mac OS, Linux or even Windows and I want to easily log them in a file, so I can replay if I have to reconfigure the machine again.
Please not that I want to do these only for some commands, so the shell history is of not use.
Ideally I would like to be able to use some kind of shell extension that logs some of the commands.
As you know if you start your bash command with a space, this command is not logged into the history.
What if I can have another prefix that would do the opposite? Is there something there that can be used for this? A solution for bash would be more than enough and if there is an already existing solution it would much better than me writing a new one.
You could do your logging in PROMPT_COMMAND, extracting the specific commands from shell history and writing them to a file.
Something like:
log () {
last_command="$(history -p \!\!)"
if [[ $last_command == " "* ]] # save commands starting with *two* spaces
then
printf "%s\n" "$last_command" >> ~/special.log
fi
}
PROMPT_COMMAND="log; $PROMPT_COMMAND"
This has problems:
PROMPT_COMMAND is run each time the prompt is printed. Just pressing Enter multiple times could cause a command to be logged multiple times.
Marking with two spaces would, of course, need you to remove ignorespace or ignoreboth from HISTCONTROL so that commands starting spaces are logged at all.
AFAICT, history is updated when the next command is read, so the command is logged after the next command returns to the prompt, since that's when the correct history is available in PROMPT_COMMAND.
All this would be easier in zsh, with a preexec hook:
preexec () {
if [[ $1 == " "* ]]
then
printf "%s\n" "$1" >> ~/special.log
fi
}
The preexec function automatically gets the command as the first argument if history is enabled, saving us a deal of trouble. It is run when the command has been read, but before it begins execution, so the timing is perfect. From the documentation:
preexec
Executed just after a command has been read and is about to be
executed. If the history mechanism is active (regardless of whether
the line was discarded from the history buffer), the string that the
user typed is passed as the first argument, otherwise it is an empty
string. The actual command that will be executed (including expanded
aliases) is passed in two different forms: the second argument is a
single-line, size-limited version of the command (with things like
function bodies elided); the third argument contains the full text
that is being executed.
$ ls
$ echo foo | echo bar
bar
$ cat ~/special.log
ls
echo foo | echo bar
A function in .bashrc can be used like a prefix:
log_this_command () {
echo "$#" >> ~/a_log_file # log the command to file
"$#" # and run the command itself
}
Caveat: this only logs expanded arguments, rather than the raw input.
Source function with the same name function screencapture {echo "used parms: $#"; command screencapture $#}
appending to log file function screencapture {echo "$(date) screencapture " $# >> ~/log.txt; command screencapture $#}
as one runs screencapture command, log entry is created and command executes as uninterfered
you could automate in creating these functions, if the list of them is like .... all of them
Is the output of a Bash command stored in any register? E.g. something similar to $? capturing the output instead of the exit status.
I could assign the output to a variable with:
output=$(command)
but that's more typing...
You can use $(!!)
to recompute (not re-use) the output of the last command.
The !! on its own executes the last command.
$ echo pierre
pierre
$ echo my name is $(!!)
echo my name is $(echo pierre)
my name is pierre
The answer is no. Bash doesn't allocate any output to any parameter or any block on its memory. Also, you are only allowed to access Bash by its allowed interface operations. Bash's private data is not accessible unless you hack it.
Very Simple Solution
One that I've used for years.
Script (add to your .bashrc or .bash_profile)
# capture the output of a command so it can be retrieved with ret
cap () { tee /tmp/capture.out; }
# return the output of the most recent command that was captured by cap
ret () { cat /tmp/capture.out; }
Usage
$ find . -name 'filename' | cap
/path/to/filename
$ ret
/path/to/filename
I tend to add | cap to the end of all of my commands. This way when I find I want to do text processing on the output of a slow running command I can always retrieve it with ret.
If you are on mac, and don't mind storing your output in the clipboard instead of writing to a variable, you can use pbcopy and pbpaste as a workaround.
For example, instead of doing this to find a file and diff its contents with another file:
$ find app -name 'one.php'
/var/bar/app/one.php
$ diff /var/bar/app/one.php /var/bar/two.php
You could do this:
$ find app -name 'one.php' | pbcopy
$ diff $(pbpaste) /var/bar/two.php
The string /var/bar/app/one.php is in the clipboard when you run the first command.
By the way, pb in pbcopy and pbpaste stand for pasteboard, a synonym for clipboard.
One way of doing that is by using trap DEBUG:
f() { bash -c "$BASH_COMMAND" >& /tmp/out.log; }
trap 'f' DEBUG
Now most recently executed command's stdout and stderr will be available in /tmp/out.log
Only downside is that it will execute a command twice: once to redirect output and error to /tmp/out.log and once normally. Probably there is some way to prevent this behavior as well.
Inspired by anubhava's answer, which I think is not actually acceptable as it runs each command twice.
save_output() {
exec 1>&3
{ [ -f /tmp/current ] && mv /tmp/current /tmp/last; }
exec > >(tee /tmp/current)
}
exec 3>&1
trap save_output DEBUG
This way the output of last command is in /tmp/last and the command is not called twice.
Yeah, why type extra lines each time; agreed.
You can redirect the returned from a command to input by pipeline, but redirecting printed output to input (1>&0) is nope, at least not for multiple line outputs.
Also you won't want to write a function again and again in each file for the same. So let's try something else.
A simple workaround would be to use printf function to store values in a variable.
printf -v myoutput "`cmd`"
such as
printf -v var "`echo ok;
echo fine;
echo thankyou`"
echo "$var" # don't forget the backquotes and quotes in either command.
Another customizable general solution (I myself use) for running the desired command only once and getting multi-line printed output of the command in an array variable line-by-line.
If you are not exporting the files anywhere and intend to use it locally only, you can have Terminal set-up the function declaration. You have to add the function in ~/.bashrc file or in ~/.profile file. In second case, you need to enable Run command as login shell from Edit>Preferences>yourProfile>Command.
Make a simple function, say:
get_prev() # preferably pass the commands in quotes. Single commands might still work without.
{
# option 1: create an executable with the command(s) and run it
#echo $* > /tmp/exe
#bash /tmp/exe > /tmp/out
# option 2: if your command is single command (no-pipe, no semi-colons), still it may not run correct in some exceptions.
#echo `"$*"` > /tmp/out
# option 3: (I actually used below)
eval "$*" > /tmp/out # or simply "$*" > /tmp/out
# return the command(s) outputs line by line
IFS=$(echo -en "\n\b")
arr=()
exec 3</tmp/out
while read -u 3 -r line
do
arr+=($line)
echo $line
done
exec 3<&-
}
So what we did in option 1 was print the whole command to a temporary file /tmp/exe and run it and save the output to another file /tmp/out and then read the contents of the /tmp/out file line-by-line to an array.
Similar in options 2 and 3, except that the commands were exectuted as such, without writing to an executable to be run.
In main script:
#run your command:
cmd="echo hey ya; echo hey hi; printf `expr 10 + 10`'\n' ; printf $((10 + 20))'\n'"
get_prev $cmd
#or simply
get_prev "echo hey ya; echo hey hi; printf `expr 10 + 10`'\n' ; printf $((10 + 20))'\n'"
Now, bash saves the variable even outside previous scope, so the arr variable created in get_prev function is accessible even outside the function in the main script:
#get previous command outputs in arr
for((i=0; i<${#arr[#]}; i++))
do
echo ${arr[i]}
done
#if you're sure that your output won't have escape sequences you bother about, you may simply print the array
printf "${arr[*]}\n"
Edit:
I use the following code in my implementation:
get_prev()
{
usage()
{
echo "Usage: alphabet [ -h | --help ]
[ -s | --sep SEP ]
[ -v | --var VAR ] \"command\""
}
ARGS=$(getopt -a -n alphabet -o hs:v: --long help,sep:,var: -- "$#")
if [ $? -ne 0 ]; then usage; return 2; fi
eval set -- $ARGS
local var="arr"
IFS=$(echo -en '\n\b')
for arg in $*
do
case $arg in
-h|--help)
usage
echo " -h, --help : opens this help"
echo " -s, --sep : specify the separator, newline by default"
echo " -v, --var : variable name to put result into, arr by default"
echo " command : command to execute. Enclose in quotes if multiple lines or pipelines are used."
shift
return 0
;;
-s|--sep)
shift
IFS=$(echo -en $1)
shift
;;
-v|--var)
shift
var=$1
shift
;;
-|--)
shift
;;
*)
cmd=$option
;;
esac
done
if [ ${#} -eq 0 ]; then usage; return 1; fi
ERROR=$( { eval "$*" > /tmp/out; } 2>&1 )
if [ $ERROR ]; then echo $ERROR; return 1; fi
local a=()
exec 3</tmp/out
while read -u 3 -r line
do
a+=($line)
done
exec 3<&-
eval $var=\(\${a[#]}\)
print_arr $var # comment this to suppress output
}
print()
{
eval echo \${$1[#]}
}
print_arr()
{
eval printf "%s\\\n" "\${$1[#]}"
}
Ive been using this to print space-separated outputs of multiple/pipelined/both commands as line separated:
get_prev -s " " -v myarr "cmd1 | cmd2; cmd3 | cmd4"
For example:
get_prev -s ' ' -v myarr whereis python # or "whereis python"
# can also be achieved (in this case) by
whereis python | tr ' ' '\n'
Now tr command is useful at other places as well, such as
echo $PATH | tr ':' '\n'
But for multiple/piped commands... you know now. :)
-Himanshu
Like konsolebox said, you'd have to hack into bash itself. Here is a quite good example on how one might achieve this. The stderred repository (actually meant for coloring stdout) gives instructions on how to build it.
I gave it a try: Defining some new file descriptor inside .bashrc like
exec 41>/tmp/my_console_log
(number is arbitrary) and modify stderred.c accordingly so that content also gets written to fd 41. It kind of worked, but contains loads of NUL bytes, weird formattings and is basically binary data, not readable. Maybe someone with good understandings of C could try that out.
If so, everything needed to get the last printed line is tail -n 1 [logfile].
Not sure exactly what you're needing this for, so this answer may not be relevant. You can always save the output of a command: netstat >> output.txt, but I don't think that's what you're looking for.
There are of course programming options though; you could simply get a program to read the text file above after that command is run and associate it with a variable, and in Ruby, my language of choice, you can create a variable out of command output using 'backticks':
output = `ls` #(this is a comment) create variable out of command
if output.include? "Downloads" #if statement to see if command includes 'Downloads' folder
print "there appears to be a folder named downloads in this directory."
else
print "there is no directory called downloads in this file."
end
Stick this in a .rb file and run it: ruby file.rb and it will create a variable out of the command and allow you to manipulate it.
If you don't want to recompute the previous command you can create a macro that scans the current terminal buffer, tries to guess the -supposed- output of the last command, copies it to the clipboard and finally types it to the terminal.
It can be used for simple commands that return a single line of output (tested on Ubuntu 18.04 with gnome-terminal).
Install the following tools: xdootool, xclip , ruby
In gnome-terminal go to Preferences -> Shortcuts -> Select all and set it to Ctrl+shift+a.
Create the following ruby script:
cat >${HOME}/parse.rb <<EOF
#!/usr/bin/ruby
stdin = STDIN.read
d = stdin.split(/\n/)
e = d.reverse
f = e.drop_while { |item| item == "" }
g = f.drop_while { |item| item.start_with? "${USER}#" }
h = g[0]
print h
EOF
In the keyboard settings add the following keyboard shortcut:
bash -c '/bin/sleep 0.3 ; xdotool key ctrl+shift+a ; xdotool key ctrl+shift+c ; ( (xclip -out | ${HOME}/parse.rb ) > /tmp/clipboard ) ; (cat /tmp/clipboard | xclip -sel clip ) ; xdotool key ctrl+shift+v '
The above shortcut:
copies the current terminal buffer to the clipboard
extracts the output of the last command (only one line)
types it into the current terminal
I have an idea that I don't have time to try to implement immediately.
But what if you do something like the following:
$ MY_HISTORY_FILE = `get_temp_filename`
$ MY_HISTORY_FILE=$MY_HISTORY_FILE bash -i 2>&1 | tee $MY_HISTORY_FILE
$ some_command
$ cat $MY_HISTORY_FILE
$ # ^You'll want to filter that down in practice!
There might be issues with IO buffering. Also the file might get too huge. One would have to come up with a solution to these problems.
I think using script command might help. Something like,
script -c bash -qf fifo_pid
Using bash features to set after parsing.
Demo for non-interactive commands only: http://asciinema.org/a/395092
For also supporting interactive commands, you'd have to hack the script binary from util-linux to ignore any screen-redrawing console codes, and run it from bashrc to save your login session's output to a file.
You can use -exec to run a command on the output of a command. So it will be a reuse of the output as an example given with a find command below:
find . -name anything.out -exec rm {} \;
you are saying here -> find a file called anything.out in the current folder, if found, remove it. If it is not found, the remaining after -exec will be skipped.
I'm having problems understanding what's going on in the following situation. I'm not familiar with UNIX pipes and UNIX at all but have read documentation and still can't understand this behaviour.
./shellcode is an executable that successfully opens a shell:
seclab$ ./shellcode
$ exit
seclab$
Now imagine that I need to pass data to ./shellcode via stdin, because this reads some string from the console and then prints "hello " plus that string. I do it in the following way (using a pipe) and the read and write works:
seclab$ printf "world" | ./shellcode
seclab$ hello world
seclab$
However, a new shell is not opened (or at least I can't see it and iteract with it), and if I run exit I'm out of the system, so I'm not in a new shell.
Can someone give some advice on how to solve this? I need to use printf because I need to input binary data to the second process and I can do it like this: printf "\x01\x02..."
When you use a pipe, you are telling Unix that the output of the command before the pipe should be used as the input to the command after the pipe. This replaces the default output (screen) and default input (keyboard). Your shellcode command doesn't really know or care where its input is coming from. It just reads the input until it reaches the EOF (end of file).
Try running shellcode and pressing Control-D. That will also exit the shell, because Control-D sends an EOF (your shell might be configured to say "type exit to quit", but it's still responding to the EOF).
There are two solutions you can use:
Solution 1:
Have shellcode accept command-line arguments:
#!/bin/sh
echo "Arguments: $*"
exec sh
Running:
outer$ ./shellcode foo
Arguments: foo
$ echo "inner shell"
inner shell
$ exit
outer$
To feed the argument in from another program, instead of using a pipe, you could:
$ ./shellcode `echo "something"`
This is probably the best approach, unless you need to pass in multi-line data. In that case, you may want to pass in a filename on the command line and read it that way.
Solution 2:
Have shellcode explicitly redirect its input from the terminal after it's processed your piped input:
#!/bin/sh
while read input; do
echo "Input: $input"
done
exec sh </dev/tty
Running:
outer$ echo "something" | ./shellcode
Input: something
$ echo "inner shell"
inner shell
$ exit
outer$
If you see an error like this after exiting the inner shell:
sh: 1: Cannot set tty process group (No such process)
Then try changing the last line to:
exec bash -i </dev/tty