After reading the Bash man pages and with respect to this post, I am still having trouble understanding what exactly the eval command does and which would be its typical uses.
For example, if we do:
$ set -- one two three # Sets $1 $2 $3
$ echo $1
one
$ n=1
$ echo ${$n} ## First attempt to echo $1 using brackets fails
bash: ${$n}: bad substitution
$ echo $($n) ## Second attempt to echo $1 using parentheses fails
bash: 1: command not found
$ eval echo \${$n} ## Third attempt to echo $1 using 'eval' succeeds
one
What exactly is happening here and how do the dollar sign and the backslash tie into the problem?
eval takes a string as its argument, and evaluates it as if you'd typed that string on a command line. (If you pass several arguments, they are first joined with spaces between them.)
${$n} is a syntax error in bash. Inside the braces, you can only have a variable name, with some possible prefix and suffixes, but you can't have arbitrary bash syntax and in particular you can't use variable expansion. There is a way of saying “the value of the variable whose name is in this variable”, though:
echo ${!n}
one
$(…) runs the command specified inside the parentheses in a subshell (i.e. in a separate process that inherits all settings such as variable values from the current shell), and gathers its output. So echo $($n) runs $n as a shell command, and displays its output. Since $n evaluates to 1, $($n) attempts to run the command 1, which does not exist.
eval echo \${$n} runs the parameters passed to eval. After expansion, the parameters are echo and ${1}. So eval echo \${$n} runs the command echo ${1}.
Note that most of the time, you must use double quotes around variable substitutions and command substitutions (i.e. anytime there's a $): "$foo", "$(foo)". Always put double quotes around variable and command substitutions, unless you know you need to leave them off. Without the double quotes, the shell performs field splitting (i.e. it splits value of the variable or the output from the command into separate words) and then treats each word as a wildcard pattern. For example:
$ ls
file1 file2 otherfile
$ set -- 'f* *'
$ echo "$1"
f* *
$ echo $1
file1 file2 file1 file2 otherfile
$ n=1
$ eval echo \${$n}
file1 file2 file1 file2 otherfile
$eval echo \"\${$n}\"
f* *
$ echo "${!n}"
f* *
eval is not used very often. In some shells, the most common use is to obtain the value of a variable whose name is not known until runtime. In bash, this is not necessary thanks to the ${!VAR} syntax. eval is still useful when you need to construct a longer command containing operators, reserved words, etc.
Simply think of eval as "evaluating your expression one additional time before execution"
eval echo \${$n} becomes echo $1 after the first round of evaluation. Three changes to notice:
The \$ became $ (The backslash is needed, otherwise it tries to evaluate ${$n}, which means a variable named {$n}, which is not allowed)
$n was evaluated to 1
The eval disappeared
In the second round, it is basically echo $1 which can be directly executed.
So eval <some command> will first evaluate <some command> (by evaluate here I mean substitute variables, replace escaped characters with the correct ones etc.), and then run the resultant expression once again.
eval is used when you want to dynamically create variables, or to read outputs from programs specifically designed to be read like this. See Eval command and security issues for examples. The link also contains some typical ways in which eval is used, and the risks associated with it.
In my experience, a "typical" use of eval is for running commands that generate shell commands to set environment variables.
Perhaps you have a system that uses a collection of environment variables, and you have a script or program that determines which ones should be set and their values. Whenever you run a script or program, it runs in a forked process, so anything it does directly to environment variables is lost when it exits. But that script or program can send the export commands to standard output.
Without eval, you would need to redirect standard output to a temporary file, source the temporary file, and then delete it. With eval, you can just:
eval "$(script-or-program)"
Note the quotes are important. Take this (contrived) example:
# activate.sh
echo 'I got activated!'
# test.py
print("export foo=bar/baz/womp")
print(". activate.sh")
$ eval $(python test.py)
bash: export: `.': not a valid identifier
bash: export: `activate.sh': not a valid identifier
$ eval "$(python test.py)"
I got activated!
The eval statement tells the shell to take eval’s arguments as commands and run them through the command-line. It is useful in a situation like below:
In your script if you are defining a command into a variable and later on you want to use that command then you should use eval:
a="ls | more"
$a
Output:
bash: command not found: ls | more
The above command didn't work as ls tried to list file with name pipe (|) and more. But these files are not there:
eval $a
Output:
file.txt
mailids
remote_cmd.sh
sample.txt
tmp
Update: Some people say one should -never- use eval. I disagree. I think the risk arises when corrupt input can be passed to eval. However there are many common situations where that is not a risk, and therefore it is worth knowing how to use eval in any case. This stackoverflow answer explains the risks of eval and alternatives to eval. Ultimately it is up to the user to determine if/when eval is safe and efficient to use.
The bash eval statement allows you to execute lines of code calculated or acquired, by your bash script.
Perhaps the most straightforward example would be a bash program that opens another bash script as a text file, reads each line of text, and uses eval to execute them in order. That's essentially the same behavior as the bash source statement, which is what one would use, unless it was necessary to perform some kind of transformation (e.g. filtering or substitution) on the content of the imported script.
I rarely have needed eval, but I have found it useful to read or write variables whose names were contained in strings assigned to other variables. For example, to perform actions on sets of variables, while keeping the code footprint small and avoiding redundancy.
eval is conceptually simple. However, the strict syntax of the bash language, and the bash interpreter's parsing order can be nuanced and make eval appear cryptic and difficult to use or understand. Here are the essentials:
The argument passed to eval is a string expression that is calculated at runtime. eval will execute the final parsed result of its argument as an actual line of code in your script.
Syntax and parsing order are stringent. If the result isn't an executable line of bash code, in scope of your script, the program will crash on the eval statement as it tries to execute garbage.
When testing you can replace the eval statement with echo and look at what is displayed. If it is legitimate code in the current context, running it through eval will work.
The following examples may help clarify how eval works...
Example 1:
eval statement in front of 'normal' code is a NOP
$ eval a=b
$ eval echo $a
b
In the above example, the first eval statements has no purpose and can be eliminated. eval is pointless in the first line because there is no dynamic aspect to the code, i.e. it already parsed into the final lines of bash code, thus it would be identical as a normal statement of code in the bash script. The 2nd eval is pointless too, because, although there is a parsing step converting $a to its literal string equivalent, there is no indirection (e.g. no referencing via string value of an actual bash noun or bash-held script variable), so it would behave identically as a line of code without the eval prefix.
Example 2:
Perform var assignment using var names passed as string values.
$ key="mykey"
$ val="myval"
$ eval $key=$val
$ echo $mykey
myval
If you were to echo $key=$val, the output would be:
mykey=myval
That, being the final result of string parsing, is what will be executed by eval, hence the result of the echo statement at the end...
Example 3:
Adding more indirection to Example 2
$ keyA="keyB"
$ valA="valB"
$ keyB="that"
$ valB="amazing"
$ eval eval \$$keyA=\$$valA
$ echo $that
amazing
The above is a bit more complicated than the previous example, relying more heavily on the parsing-order and peculiarities of bash. The eval line would roughly get parsed internally in the following order (note the following statements are pseudocode, not real code, just to attempt to show how the statement would get broken down into steps internally to arrive at the final result).
eval eval \$$keyA=\$$valA # substitution of $keyA and $valA by interpreter
eval eval \$keyB=\$valB # convert '$' + name-strings to real vars by eval
eval $keyB=$valB # substitution of $keyB and $valB by interpreter
eval that=amazing # execute string literal 'that=amazing' by eval
If the assumed parsing order doesn't explain what eval is doing enough, the third example may describe the parsing in more detail to help clarify what is going on.
Example 4:
Discover whether vars, whose names are contained in strings, themselves contain string values.
a="User-provided"
b="Another user-provided optional value"
c=""
myvarname_a="a"
myvarname_b="b"
myvarname_c="c"
for varname in "myvarname_a" "myvarname_b" "myvarname_c"; do
eval varval=\$$varname
if [ -z "$varval" ]; then
read -p "$varname? " $varname
fi
done
In the first iteration:
varname="myvarname_a"
Bash parses the argument to eval, and eval sees literally this at runtime:
eval varval=\$$myvarname_a
The following pseudocode attempts to illustrate how bash interprets the above line of real code, to arrive at the final value executed by eval. (the following lines descriptive, not exact bash code):
1. eval varval="\$" + "$varname" # This substitution resolved in eval statement
2. .................. "$myvarname_a" # $myvarname_a previously resolved by for-loop
3. .................. "a" # ... to this value
4. eval "varval=$a" # This requires one more parsing step
5. eval varval="User-provided" # Final result of parsing (eval executes this)
Once all the parsing is done, the result is what is executed, and its effect is obvious, demonstrating there is nothing particularly mysterious about eval itself, and the complexity is in the parsing of its argument.
varval="User-provided"
The remaining code in the example above simply tests to see if the value assigned to $varval is null, and, if so, prompts the user to provide a value.
I originally intentionally never learned how to use eval, because most people will recommend to stay away from it like the plague. However I recently discovered a use case that made me facepalm for not recognizing it sooner.
If you have cron jobs that you want to run interactively to test, you might view the contents of the file with cat, and copy and paste the cron job to run it. Unfortunately, this involves touching the mouse, which is a sin in my book.
Lets say you have a cron job at /etc/cron.d/repeatme with the contents:
*/10 * * * * root program arg1 arg2
You cant execute this as a script with all the junk in front of it, but we can use cut to get rid of all the junk, wrap it in a subshell, and execute the string with eval
eval $( cut -d ' ' -f 6- /etc/cron.d/repeatme)
The cut command only prints out the 6th field of the file, delimited by spaces. Eval then executes that command.
I used a cron job here as an example, but the concept is to format text from stdout, and then evaluate that text.
The use of eval in this case is not insecure, because we know exactly what we will be evaluating before hand.
I've recently had to use eval to force multiple brace expansions to be evaluated in the order I needed. Bash does multiple brace expansions from left to right, so
xargs -I_ cat _/{11..15}/{8..5}.jpg
expands to
xargs -I_ cat _/11/8.jpg _/11/7.jpg _/11/6.jpg _/11/5.jpg _/12/8.jpg _/12/7.jpg _/12/6.jpg _/12/5.jpg _/13/8.jpg _/13/7.jpg _/13/6.jpg _/13/5.jpg _/14/8.jpg _/14/7.jpg _/14/6.jpg _/14/5.jpg _/15/8.jpg _/15/7.jpg _/15/6.jpg _/15/5.jpg
but I needed the second brace expansion done first, yielding
xargs -I_ cat _/11/8.jpg _/12/8.jpg _/13/8.jpg _/14/8.jpg _/15/8.jpg _/11/7.jpg _/12/7.jpg _/13/7.jpg _/14/7.jpg _/15/7.jpg _/11/6.jpg _/12/6.jpg _/13/6.jpg _/14/6.jpg _/15/6.jpg _/11/5.jpg _/12/5.jpg _/13/5.jpg _/14/5.jpg _/15/5.jpg
The best I could come up with to do that was
xargs -I_ cat $(eval echo _/'{11..15}'/{8..5}.jpg)
This works because the single quotes protect the first set of braces from expansion during the parsing of the eval command line, leaving them to be expanded by the subshell invoked by eval.
There may be some cunning scheme involving nested brace expansions that allows this to happen in one step, but if there is I'm too old and stupid to see it.
You asked about typical uses.
One common complaint about shell scripting is that you (allegedly) can't pass by reference to get values back out of functions.
But actually, via "eval", you can pass by reference. The callee can pass back a list of variable assignments to be evaluated by the caller. It is pass by reference because the caller can allowed to specify the name(s) of the result variable(s) - see example below. Error results can be passed back standard names like errno and errstr.
Here is an example of passing by reference in bash:
#!/bin/bash
isint()
{
re='^[-]?[0-9]+$'
[[ $1 =~ $re ]]
}
#args 1: name of result variable, 2: first addend, 3: second addend
iadd()
{
if isint ${2} && isint ${3} ; then
echo "$1=$((${2}+${3}));errno=0"
return 0
else
echo "errstr=\"Error: non-integer argument to iadd $*\" ; errno=329"
return 1
fi
}
var=1
echo "[1] var=$var"
eval $(iadd var A B)
if [[ $errno -ne 0 ]]; then
echo "errstr=$errstr"
echo "errno=$errno"
fi
echo "[2] var=$var (unchanged after error)"
eval $(iadd var $var 1)
if [[ $errno -ne 0 ]]; then
echo "errstr=$errstr"
echo "errno=$errno"
fi
echo "[3] var=$var (successfully changed)"
The output looks like this:
[1] var=1
errstr=Error: non-integer argument to iadd var A B
errno=329
[2] var=1 (unchanged after error)
[3] var=2 (successfully changed)
There is almost unlimited band width in that text output! And there are more possibilities if the multiple output lines are used: e.g., the first line could be used for variable assignments, the second for continuous 'stream of thought', but that's beyond the scope of this post.
In the question:
who | grep $(tty | sed s:/dev/::)
outputs errors claiming that files a and tty do not exist. I understood this to mean that tty is not being interpreted before execution of grep, but instead that bash passed tty as a parameter to grep, which interpreted it as a file name.
There is also a situation of nested redirection, which should be handled by matched parentheses which should specify a child process, but bash is primitively a word separator, creating parameters to be sent to a program, therefore parentheses are not matched first, but interpreted as seen.
I got specific with grep, and specified the file as a parameter instead of using a pipe. I also simplified the base command, passing output from a command as a file, so that i/o piping would not be nested:
grep $(tty | sed s:/dev/::) <(who)
works well.
who | grep $(echo pts/3)
is not really desired, but eliminates the nested pipe and also works well.
In conclusion, bash does not seem to like nested pipping. It is important to understand that bash is not a new-wave program written in a recursive manner. Instead, bash is an old 1,2,3 program, which has been appended with features. For purposes of assuring backward compatibility, the initial manner of interpretation has never been modified. If bash was rewritten to first match parentheses, how many bugs would be introduced into how many bash programs? Many programmers love to be cryptic.
As clearlight has said, "(p)erhaps the most straightforward example would be a bash program that opens another bash script as a text file, reads each line of text, and uses eval to execute them in order". I'm no expert, but the textbook I'm currently reading (Shell-Programmierung by Jürgen Wolf) points to one particular use of this that I think would be a valuable addition to the set of potential use cases collected here.
For debugging purposes, you may want to go through your script line by line (pressing Enter for each step). You could use eval to execute every line by trapping the DEBUG signal (which I think is sent after every line):
trap 'printf "$LINENO :-> " ; read line ; eval $line' DEBUG
I like the "evaluating your expression one additional time before execution" answer, and would like to clarify with another example.
var="\"par1 par2\""
echo $var # prints nicely "par1 par2"
function cntpars() {
echo " > Count: $#"
echo " > Pars : $*"
echo " > par1 : $1"
echo " > par2 : $2"
if [[ $# = 1 && $1 = "par1 par2" ]]; then
echo " > PASS"
else
echo " > FAIL"
return 1
fi
}
# Option 1: Will Pass
echo "eval \"cntpars \$var\""
eval "cntpars $var"
# Option 2: Will Fail, with curious results
echo "cntpars \$var"
cntpars $var
The curious results in option 2 are that we would have passed two parameters as follows:
First parameter: "par1
Second parameter: par2"
How is that for counter intuitive? The additional eval will fix that.
It was adapted from another answer on How can I reference a file for variables using Bash?
I executed a background process that was obtained as a parameter and didn't success to get the process's name after the execution.
I do the following:
#! /bin/bash
filePath=$1
$filePath > log.txt &
echo `jobs -l`
Actual result:
[1]+ 2381 Running $filePath > log.txt &
Expected result:
[1]+ 2381 Running /home/user/Desktop/script.sh > log.txt &
The best answer is don't; job control is a feature designed for interactive use, and is not guaranteed to be available at all in noninteractive shells, much less guaranteed to behave in any useful or meaningful way. However, if you insist, you can use printf %q to generate an eval-safe string with the post-expansion form of your variables, and then use eval to run it as code:
#!/bin/bash
printf -v logfile_q '%q' "${log:-log.txt}" # use "$logfile", or default to log.txt
printf -v cmd_q '%q ' "$#" # quote our arguments into one eval-safe string
eval "$cmd_str >$logfile_q &" # Parts that aren't hardcoded must be printf-q'd for safety.
jobs -l
Note that I added some extra configurability for the sake of demonstration -- it's okay to have >log.txt inside your eval'd code, but it's not safe to have >$logfile, because if logfile=$'foo$(rm -rf ~)\'$(rm -rf ~)\'' (a perfectly legal filename!) then you're going to lose your home directory. Thus, any variables needing to be used inside an argument to eval need to be escaped with printf %q beforehand.
When my bash scripts start getting complex, I usually break them up into functions. This applies especially to complex pipes, as a sequence of complicated pipe commands (e.g. containing while-loops) can quickly become hard to read. Even more so when parallelization is wanted, where xargs is very helpful.
I know that I can export functions to a subshell with export -f, thus in a simple case I can do
export -f myfunction
some-command | xargs -Iline bash -c "myfunction 'line'"
but if the myfunction depends on other functions this becomes hard to maintain -- every time the function changes such that the functions needed by the subshell for executing myfunction change, the export statement would have to be changed -- that seems pretty error prone.
Is there some general way to export functions for use by subshells? I was thinking about something along the lines of an "export all defined functions" command, which would then allow a code structure like
main() { ... }
func1 () { ... }
func2 () { ... }
<export all functions>
main "$#"
Your question asks only about exporting functions. This is easy in bash, see below.
Your question title/subject implies using functions in xargs, as though they were a script;
I don't know that xargs can "call" a bash function directly, but you can of course wrap
your use of the exported function(s) in a script called by xargs, see below.
First, a function to list functions. User functions by default and -v to list all functions:
lsfns () {
case "$1" in
-v | v*)
# verbose:
set | grep '()' --color=always
;;
*)
declare -F | cut -d" " -f3 | egrep -v "^_"
;;
esac
}
Next a function to export all user functions:
exportfns () { export -f $(lsfns); }
or just put export -f $(lsfns) in your .bashrc.
Example script doit.sh:
#!/bin/bash
lsfns "$#" # make use of function exported by parent shell :)
Example command line (after chmod a+rx doit.sh):
echo -v | xargs doit.sh
Compare with
echo "" | xargs doit.sh
EDIT 1: responding further to kdb's comment/answer below ("running into situations where exporting functions does not work at all"):
Export of shell functions is not Posix compatible - i.e. it only works with Bash and presumably other shells such as Zsh, Ksh etc.
That is, in Dash, and "standard" Posix shells not providing "export -f", we cannot export functions, AND if we export a function say in Bash, then run a script which starts with the sh-bang e.g. "#!/bin/dash", that script will NOT be able to use the "exported" functions from the parent shell, since functions exported to the "process environment" by Bash, are not recognised by Dash.
EDIT 2: responding further to OP comment "but if the myfunction depends on other functions this becomes hard to maintain":
This is probably a situation where one could make good use of the shell source command (alias "."), e.g.:
. ~/etc/my-functions.sh; myMain ...
And similarly, if you "live" in functions rather than script files, e.g. by calling myMain when you need to, then the first line of this function can be to source your function library;
since this would be excess overhead in the "running a script regularly" case, myMain becomes the command-line stub function, which (re)loads your function library, and calls the actuallyDoit function (which would also be called from inside your script, if you have a script file).
Enjoy
Zenaan
This seems to work to print all the function names. It feels fragile, so test it out
declare -f | grep -oP '^\S+(?=\s*\(\))'
export -f $(compgen -A function)
Since receiving the answer, I found many cases where a different technique proofed preferable: Making the script invoke itself. A simple example would be
# Print hash and disk usage for each argument
if [[ $1 == run ]]; then
shift 1
printf "%s\0" "$#" | xargs -0 -n 1 -P "$NUMBER_OF_PROCESSORS" -- "$0" printpar
elif [[ $1 == printpar ]]; then
echo ":: $(cat "$2" | sha1sum) $(du -sh "$2")"
else
echo "Invalid first parameter '$1'"
exit 1
fi
In real-world examples I'd either make assumptions about the arguments (e.g. using __SUCH__ a shape for self-call keywords) or hide recursive invocations behind an undocumented --command-line-switch.
Exporting functions is generally more elegant, but for large numbers of function it can get prohibitively slow and I remember running into issues, where it failed entirely.
Is it possible to pass command line arguments to shell script as name value pairs, something like
myscript action=build module=core
and then in my script, get the variable like
$action and process it?
I know that $1....and so on can be used to get variables, but then won't be name value like pairs. Even if they are, then the developer using the script will have to take care of declaring variables in the same order. I do not want that.
This worked for me:
for ARGUMENT in "$#"
do
KEY=$(echo $ARGUMENT | cut -f1 -d=)
KEY_LENGTH=${#KEY}
VALUE="${ARGUMENT:$KEY_LENGTH+1}"
export "$KEY"="$VALUE"
done
# from this line, you could use your variables as you need
cd $FOLDER
mkdir $REPOSITORY_NAME
Usage
bash my_scripts.sh FOLDER="/tmp/foo" REPOSITORY_NAME="stackexchange"
STEPS and REPOSITORY_NAME are ready to use in the script.
It does not matter what order the arguments are in.
Changelog
v1.0.0
In the Bourne shell, there is a seldom-used option '-k' which automatically places any values specified as name=value on the command line into the environment. Of course, the Bourne/Korn/POSIX shell family (including bash) also do that for name=value items before the command name:
name1=value1 name2=value2 command name3=value3 -x name4=value4 abc
Under normal POSIX-shell behaviour, the command is invoked with name1 and name2 in the environment, and with four arguments. Under the Bourne (and Korn and bash, but not POSIX) shell -k option, it is invoked with name1, name2, name3, and name4 in the environment and just two arguments. The bash manual page (as in man bash) doesn't mention the equivalent of -k but it works like the Bourne and Korn shells do.
I don't think I've ever used it (the -k option) seriously.
There is no way to tell from within the script (command) that the environment variables were specified solely for this command; they are simply environment variables in the environment of that script.
This is the closest approach I know of to what you are asking for. I do not think anything equivalent exists for the C shell family. I don't know of any other argument parser that sets variables from name=value pairs on the command line.
With some fairly major caveats (it is relatively easy to do for simple values, but hard to deal with values containing shell meta-characters), you can do:
case $1 in
(*=*) eval $1;;
esac
This is not the C shell family. The eval effectively does the shell assignment.
arg=name1=value1
echo $name1
eval $arg
echo $name1
env action=build module=core myscript
You said you're using tcsh. For Bourne-based shells, you can drop the "env", though it's harmless to leave it there. Note that this applies to the shell from which you run the command, not to the shell used to implement myscript.
If you specifically want the name=value pairs to follow the command name, you'll need to do some work inside myscript.
It's quite an old question, but still valid
I have not found the cookie cut solution. I combined the above answers. For my needs I created this solution; this works even with white space in the argument's value.
Save this as argparse.sh
#!/bin/bash
: ${1?
'Usage:
$0 --<key1>="<val1a> <val1b>" [ --<key2>="<val2a> <val2b>" | --<key3>="<val3>" ]'
}
declare -A args
while [[ "$#" > "0" ]]; do
case "$1" in
(*=*)
_key="${1%%=*}" && _key="${_key/--/}" && _val="${1#*=}"
args[${_key}]="${_val}"
(>&2 echo -e "key:val => ${_key}:${_val}")
;;
esac
shift
done
(>&2 echo -e "Total args: ${#args[#]}; Options: ${args[#]}")
## This additional can check for specific key
[[ -n "${args['path']+1}" ]] && (>&2 echo -e "key: 'path' exists") || (>&2 echo -e "key: 'path' does NOT exists");
#Example: Note, arguments to the script can have optional prefix --
./argparse.sh --x="blah"
./argparse.sh --x="blah" --yy="qwert bye"
./argparse.sh x="blah" yy="qwert bye"
Some interesting use cases for this script:
./argparse.sh --path="$(ls -1)"
./argparse.sh --path="$(ls -d -1 "$PWD"/**)"
Above script created as gist, Refer: argparse.sh
Extending on Jonathan's answer, this worked nicely for me:
#!/bin/bash
if [ "$#" -eq "0" ]; then
echo "Error! Usage: Remind me how this works again ..."
exit 1
fi
while [[ "$#" > "0" ]]
do
case $1 in
(*=*) eval $1;;
esac
shift
done
I have the following (bash) shell script, that I would ideally use to kill multiple processes by name.
#!/bin/bash
kill `ps -A | grep $* | awk '{ print $1 }'`
However, while this script works is one argument is passed:
end chrome
(the name of the script is end)
it does not work if more than one argument is passed:
$end chrome firefox
grep: firefox: No such file or directory
What is going on here?
I thought the $* passes multiple arguments to the shell script in sequence. I'm not mistyping anything in my input - and the programs I want to kill (chrome and firefox) are open.
Any help is appreciated.
Remember what grep does with multiple arguments - the first is the word to search for, and the remainder are the files to scan.
Also remember that $*, "$*", and $# all lose track of white space in arguments, whereas the magical "$#" notation does not.
So, to deal with your case, you're going to need to modify the way you invoke grep. You either need to use grep -F (aka fgrep) with options for each argument, or you need to use grep -E (aka egrep) with alternation. In part, it depends on whether you might have to deal with arguments that themselves contain pipe symbols.
It is surprisingly tricky to do this reliably with a single invocation of grep; you might well be best off tolerating the overhead of running the pipeline multiple times:
for process in "$#"
do
kill $(ps -A | grep -w "$process" | awk '{print $1}')
done
If the overhead of running ps multiple times like that is too painful (it hurts me to write it - but I've not measured the cost), then you probably do something like:
case $# in
(0) echo "Usage: $(basename $0 .sh) procname [...]" >&2; exit 1;;
(1) kill $(ps -A | grep -w "$1" | awk '{print $1}');;
(*) tmp=${TMPDIR:-/tmp}/end.$$
trap "rm -f $tmp.?; exit 1" 0 1 2 3 13 15
ps -A > $tmp.1
for process in "$#"
do
grep "$process" $tmp.1
done |
awk '{print $1}' |
sort -u |
xargs kill
rm -f $tmp.1
trap 0
;;
esac
The use of plain xargs is OK because it is dealing with a list of process IDs, and process IDs do not contain spaces or newlines. This keeps the simple code for the simple case; the complex case uses a temporary file to hold the output of ps and then scans it once per process name in the command line. The sort -u ensures that if some process happens to match all your keywords (for example, grep -E '(firefox|chrome)' would match both), only one signal is sent.
The trap lines etc ensure that the temporary file is cleaned up unless someone is excessively brutal to the command (the signals caught are HUP, INT, QUIT, PIPE and TERM, aka 1, 2, 3, 13 and 15; the zero catches the shell exiting for any reason). Any time a script creates a temporary file, you should have similar trapping around the use of the file so that it will be cleaned up if the process is terminated.
If you're feeling cautious and you have GNU Grep, you might add the -w option so that the names provided on the command line only match whole words.
All the above will work with almost any shell in the Bourne/Korn/POSIX/Bash family (you'd need to use backticks with strict Bourne shell in place of $(...), and the leading parenthesis on the conditions in the case are also not allowed with Bourne shell). However, you can use an array to get things handled right.
n=0
unset args # Force args to be an empty array (it could be an env var on entry)
for i in "$#"
do
args[$((n++))]="-e"
args[$((n++))]="$i"
done
kill $(ps -A | fgrep "${args[#]}" | awk '{print $1}')
This carefully preserves spacing in the arguments and uses exact matches for the process names. It avoids temporary files. The code shown doesn't validate for zero arguments; that would have to be done beforehand. Or you could add a line args[0]='/collywobbles/' or something similar to provide a default - non-existent - command to search for.
To answer your question, what's going on is that $* expands to a parameter list, and so the second and later words look like files to grep(1).
To process them in sequence, you have to do something like:
for i in $*; do
echo $i
done
Usually, "$#" (with the quotes) is used in place of $* in cases like this.
See man sh, and check out killall(1), pkill(1), and pgrep(1) as well.
Look into pkill(1) instead, or killall(1) as #khachik comments.
$* should be rarely used. I would generally recommend "$#". Shell argument parsing is relatively complex and easy to get wrong. Usually the way you get it wrong is to end up having things evaluated that shouldn't be.
For example, if you typed this:
end '`rm foo`'
you would discover that if you had a file named 'foo' you don't anymore.
Here is a script that will do what you are asking to have done. It fails if any of the arguments contain '\n' or '\0' characters:
#!/bin/sh
kill $(ps -A | fgrep -e "$(for arg in "$#"; do echo "$arg"; done)" | awk '{ print $1; }')
I vastly prefer $(...) syntax for doing what backtick does. It's much clearer, and it's also less ambiguous when you nest things.