I write a code in Bash script and the Linux does not run it correctly and printed character instead of character’s value.
Can anyone help me?
Aside from the confusion between backtick and ', you are also over-using the sub-shell syntax. You do not need to use echo $(cat $LOOP). You can just run cat $LOOP directly.
#!/bin/bash
for FILE in $(ls); do
echo "Here is ${file}:"
cat ${FILE}
echo ""
done
A couple of points of style as well:
Name your variables after the thing they represent. The loop is iterating over files in the current directory, so the name FILE is more descriptive than LOOP.
It is a good idea to get in the habit of enclosing your variable references in ${ ... } instead of just prefixing them with $. In simple scripts like this, it does not make a difference, but when your scripts get more complicated, you can get into trouble when you do not clearly delineate variable names.
Related
The following simplified version of a script I'll call logit obviously just appends everything but $1 in a text file, so I can keep track of time like this:
$ logit Started work on default theme
But bash expansion gets confused by quotes of any kind. What I'd like is to do things like
$ logit Don't forget a dark mode
But when that happens of course shell expansion rules cause a burp:
quote>
I know this works:
# Yeah yeah I can enclose it in quotes but I'd prefer not to
$ logit "Don't forget a dark mode"
Is there any way to somehow collect the remainder of the command line before bash gets to it, without having to use quotes around my command line?
Here's a minimal working version of the script.
#!/bin/bash
log_file=~/log.txt
now=$(date +"%T %r")
echo "${now} ${#:1}" >> $log_file
Is there any way to somehow collect the remainder of the command line before bash gets to it, without having to use quotes around my command line?
No. There is no "before bash gets into it" time. Bash reads the input you are typing, Bash parses the input you are typing, there is nothing in between or "before". There is only Bash.
You can: use a different shell or write your own. Note that quotes parsing like in shell is very common, you may consider that it could be better for you to understand and get used to it.
you can use a backslash "\" before the single quote
$ logit Don\'t forget a dark mode
NOTE: The goal of this question is to find a suitable character sequence for an effective placeholder substitution in a bash script, not finding if a command is evaluated or not.
I have a skeleton named my_script.skelof a bash script in which I have to put a placeholder. I want to find a placeholder sequence that can be safely substituted (I mean that there aren't any clashes with other bash commands or other pathological substitutions, see A non-safe example for an example).
I've figured out on my own that enveloping placeholder_name within #~ and ~# seems a good solution, but I'm not sure that this solution is safe in every possible case.
A non-safe example
One can decide to use /placeholder_name/. So my_dumb_script.skel is:
#!/bin/bash
AN_INNOCENT_PATH="/a/simple/placeholder_name/path"
echo /placeholder_name/
The goal is to replace only /placeholder_name/ in the echo command. If now I use sed on the placeholder:
sed 's%/placeholder_name/%foobar%g' my_dumb_script.skel > output.bash
The output could be unexpected:
#!/bin/bash
AN_INNOCENT_PATH="/a/simplefoobarpath"
echo foobar
In this case we've obtained an unwanted substitution inside AN_INNOCENT_PATH, since it's easy to pattern-match on placeholders that contains the / character. I know that it seems very dumb, but you cannot know how people will use your code in the future (and someone could create a folder named placeholder_name).
A safe example that uses #~
In this case my_better_script.skel is the following one:
#!/bin/bash
AN_INNOCENT_PATH="/a/simple/placeholder_name/path"
echo #~placeholder_name~#
And now we can use sed:
sed 's%#~placeholder_name~#%foobar%g' my_better_script.skel > output.bash
The output now is better:
#!/bin/bash
AN_INNOCENT_PATH="/a/simple/placeholder_name/path"
echo foobar
Now everything works as intended.
You can use type to check if a command will evaluate.
$ placeholder1="testing"
$ placeholder2="test"
$ type $placeholder1
-bash: type: testing: not found
$ type $placeholder2
test is a shell builtin
Say I have a bash script file config.sh. It's meant to be source'd by other scripts and variables defined is used as customization of the upper-level scripts.
The problem is, if config.sh has a temporary variable and its name conflicts with upper-level scripts' variable, it breaks the upper-level one.
config.sh:
TMP1=abc
CONFIG_INPUT_DIR="$TMP1"/in
CONFIG_OUTPUT_DIR="$TMP1"/out
upper-level script:
TMP1=def
source config.sh
echo $TMP1
The last echo prints abc, not def.
Solution 1
My current solution is to append a random string to the temporary variable name to make it almost impossible to conflict. e.g:
TMP1_vFc9Uiew=abc
CONFIG_INPUT_DIR="$TMP1_vFc9Uiew"/in
CONFIG_OUTPUT_DIR="$TMP1_vFc9Uiew"/out
unset TMP1_vFc9Uiew
which is painful and makes the code hard to read, in addition not to be perfect.
Solution 2 using local keyword
After some searching, I've come to know local keyword.
But when I simply declare TMP1 as local, bash complains that config.sh: line 1: local: can only be used in a function.
So my another solution is to enclose whole config script as a function:
function config_func_rZ0Yqkpm() {
local TMP1=abc
CONFIG_INPUT_DIR="$TMP1"/in
CONFIG_OUTPUT_DIR="$TMP1"/out
}
config_func_rZ0Yqkpm
unset config_func_rZ0Yqkpm
which is better than previous solution in maintainability and readability, but there's some possibility to conflict as well as solution 1.
Question
I want to know more robust and smart solution without any possibility to conflict.
Thanks.
A trick I learned from the keychain utility is using one program to build a source-able file containing just the variables that you want to export from your program. You could modify your script to echo the variables you want to set and then source the output from your program:
$ echo $FOO
$ source <(echo FOO=bar)
$ echo $FOO
bar
$
I used echo FOO=bar to simulate the larger script; your program is probably more involved. The important part is that you must modify your program to output the variables and values you would like to set, rather than just setting them. This lets you decide which variables to expose and which ones to hold private at the cost of another shell process.
You could avoid variables and use functions in config.sh to hold your values:
get_dirname() { echo "abc"; }
CONFIG_INPUT_DIR="$(get_dirname)/in"
CONFIG_OUTPUT_DIR="$(get_dirname)/out"
unset -f get_dirname
If you're still concerned about name collision for functions, this doesn't really help you.
The "ssh-agent" method:
config.sh
#!/bin/bash
TMP=abc
printf "CONFIG_INPUT_DIR=%s/in\n" "$TMP"
printf "CONFIG_OUTPUT_DIR=%s/out\n" "$TMP"
main program:
TMP1=def
eval "$(config.sh)"
echo "$TMP1"
I am using the sh 3.2 in Mac Os X. I have a file test.conf
config1="Configuration 1"
config2="a lot of text"
config3=...
So I only need to get the config1= and config2= parameter. How can I set a variable, that I can do this:
> echo $variable
Configuration 1
So simple, but I am not doing it work.
the sommand you are looking for is source
source test.conf
echo $config1 #echoes Configuration 1
if you need to have config1 in variable, add
varible=$config1
At a rough guess...
export `grep 'config1=' /your/config/file`
export `grep 'config2=' /your/config/file`
But remember if you put this in a shell script file, then you'll need to eval the file rather than execute it to set the variables in the current shell instance.
You could do this:
variable=`sed -n 's/^config1=//p'`
Or if you are attempting to evaluate certain parts of your file, try something like
eval `grep ^config1= test.conf`
to have config1=Configuration 1 evaluated by the current shell. (With the example you provided, this will cause a syntax error, because the value cannot contain unquoted whitespace.)
I generally recommend beginners to stay away from backticks, but this is a situation where they are a good answer.
How can I set variables that work everywhere? My .bashrc has:
Questions='/Users/User/Stackoverflow/Questions'
Address='My address'
My file has:
$Questions
$Addres
The command "$ cat my_file" in Shell prints "$Questions" and "$Address", instead of "/Users/User/Stackoverflow/Questions" and "My address". Other places where I would like have the variables are Email and Browser. But I cannot get them working.
How can I have my variables to work in every program?
cat doesn't interpret variables. It simply prints out the contents of a file, byte-for-byte.
If you want to be able to print out the values of the variables with my_file, I would suggest changing it to read
echo "$Questions"
echo "$Address"
Then you can "source" it (kind of like running it in the current shell environment) with
$ source my_file
or
$ . my_file
You might also have to use export in .bashrc, like so:
export Questions='/Users/User/Stackoverflow/Questions'
export Address='My address'
How can I have my variables to work in every program?
You can't. Bash and cat are two separate programs. You set a bash variable, it doesn't mean that cat will behave like bash to interpret it. $VARNAME is a shell syntax, cat is a different program, that share almost nothing with the shell.
You can export the shell variable as an environment variable, but cat is not programmed to replace any text templates, it goes way beyond its purpose.
Instead, you may use sed to perform text template substitutions:
sed -e "s|#QUESTIONS#|$Questions|g; s|#ADDRESS#|$Address|g" file.txt
This will replace all instances of #QUESTIONS# and #ANSWERS# in the file with the contents of $Questions and $Address shell variables. Note that these shell variables must not contain any pipe ("|") symbols, since the suggestion uses them as delimiters.
You can get the "cat" thing to work using some nasty hackery:
eval "$(printf 'cat << END\n%s\nEND' "$(< foo)")"
Where "foo" is the file that contains your text you want the bash parameters expanded from. This solution basically just converts the text into a here document, which does expand bash parameters.
cat <<END
[your text]
END
Limitations:
You can't have a line with just "END" in the text file or the solution will break. It'll think the line with "END" in the text file ends the here document instead of the END in the printf command, and the ouput will end early.
TBH:
This is something you just shouldn't want to do. If you want to make template files, go find a templating system that's built for this. You shouldn't be raping bash into doing something that it isn't built to do. It's a scripting language, not a templating system. It's built to parse scripts with a well defined syntax, not arbitrary text files.
You can't. In order to do that, you'd need the cooperation of every email client writer, every browser writer, every utility writer.
Type env see if the variables exist.
If so, try calling them with ${VAR_NAME}.
After re-iterating I now see your problem. You just can't have a text file, cat out it's content and expect the environments variables to be parsed. You just can't.
If it was a bash script file, and you were to run it, you could echo out the variables and they would be parsed like you want.
From your comment on Paul Tomblin's answer:
Are you sure? I have heard that you can have all kind of things like RSS-reader in Emacs. Perhaps, there is a better cooperation. I am a VIM-user, so I don't know. If someone knows whether Emacs has great cooperation between programs, please do not hesitate to share your knowledge. – UnixBasics (3 mins ago)
Do you want (or would you be satisfied with) an editor that can expand your environment variables?
That is a different (i.e. simpler, and possible) problem.
On purely theoretical level, I suppose a hacked filesystem could do what you want, but it would certainly break all kinds of binary storage. So we add a filesystem flag for text (expandable) and non-text file types. And we'd need a way for the filesystem to know what set of variable to expand, and ad nauseum...
Just add to your ~/.profile or to ~/.bashrc:
export Questions='/Users/User/Stackoverflow/Questions'
export Address='My address'