I'm writing a shell script called myShellScript.sh inside of which I have the following text:
echo *** Print out this line ****
diff <(./myProgram) <(./otherProgram)
However, when I run sh myShellScript.sh I get the following error:
-bash-4.2$ sh myShellScript.sh
myShellScript.sh **** Print out this line **** myShellScript.sh
myShellScript.sh: line 2: syntax error near unexpected token `('
myShellScript.sh: line 2: `diff <(./myProgram) <(./otherProgram)'
Process substitution with the <(...) operator is a bash feature. You're getting that error message because your script is getting executed as something else (for example dash), or an older version of bash, or bash running in POSIX-compatibility mode with non-POSIX features like process substitution disabled (thanks, #chepner!)
If you want to execute the script with a full-featured bash, you have two options:
Run the script with bash:
bash myShellScript.sh
Set the first line of the script to #!/bin/bash (or whatever is the path to bash in your system), and run the script like this:
./myShellScript.sh
You need to execute your script with bash, not with sh.
You are using process substitution, which is not a standard POSIX shell feature. sh is a POSIX-compatible shell, so it does not support language extensions like process substitution. Bash will run with POSIX compatibility enabled if it is invoked as sh.
Therefore, you should execute scripts that require Bash-specific features using bash.
You clearly seem to be using bash, but for anyone reading this that needs to use a shell without support for process substitution, you can use the following:
# Instead of diff <(./myProgram) <(./otherProgram)
# A pair of named pipes to avoid using disk space
# for the output of myProgram and otherProgram
mkfifo myProgram.output
mkfifo otherProgram.output
./myProgram > myProgram.output &
./otherProgram > otherProgram.output &
diff myProgram.output otherProgram.output
rm myProgram.output otherProgram.output
This is nearly identical to how bash might perform process substitution on some platforms.
Related
I want to run this script:
#!/bin/bash
echo <(true)
I run it as:
sh file.sh
And I get "Syntax error: "(" unexpected" . I found some similar situations but still can't solve this.
I'm a beginner at shell scripting , but as I understand:
the shebang I use is correct and chooses the bash shell , so the process substitution syntax should work
I try the same from the command line and it works. I checked with echo $0 and it gives me "bash" , so what's the difference from running the command in the command line and from a script that invokes the same shell?
Maybe it's something simple, but I couldn't find an explanation or solution.
You should run your script with bash, i.e. either bash ./script.sh or making use of the shebang by ./script.sh after setting it to executable. Only running it with sh ./script.sh do I get your error, as commented by Cyrus.
See also: role of shebang at unix.SE
Remove export POSIXLY_CORRECT=1 from your ~/.bashrc or ~/.profile (etc.) files.
The issue is that process substitution is an added bash feature that is not part of the posix standards.
sh file.sh
errorsh: 3: Syntax error: "(" unexpected
solution:
bash file.sh
I have a script which runs fine when executed in Bash shell (with Red Hat Linux), however this same script which fails on a Solaris 10 (DB) server where ksh is being used to execute this script. This script basically reads line by line from a file and executes a stored proc (in Oracle). Below is my script :
#/bin/sh
for i in $(cat subscriber.txt); do
SUBSCRIBER_ID="'$i'"
sqlplus -s myuser/myuser <<EOF
execute delete_learnings($SUBSCRIBER_ID);
commit;
EXIT
EOF
done
The error I get is :
./removeLearnings.sh: syntax error at line 3: `$' unexpected
Any idea what might be going wrong? Should I change the script to have the ksh? I am not able to debug on this machine since it's a customer environment (which I don't have access to).
The issue is the $(...) construction which is POSIX compliant but unsupported by the legacy Bourne shell which /bin/sh is on Solaris 10 and older.
You can either replace your shebang to call the Solaris POSIX compliant shell:
#!/usr/xpg4/bin/sh
or use this legacy syntax (less recommended):
for i in `cat subscriber.txt`; do
you are trying to execute a sh( bourne shell) script on ksh (Korn shell). Try changing the shebang (#!/bin/bash) to (#!/bin/ksh)
Looping over text files with for is a bad idea, anyway. See http://mywiki.wooledge.org/BashFAQ/001- the recommended syntax is more portable, too:
while read stuff; do
: things with "$stuff"
done <subscriber.txt
You would normally use read -r but I don't know if that's available on Solaris.
However, very often, a shell loop is altogether the wrong approach. A single SQL invocation is a lot better and more robust:
( sed 's/.*/execute delete_learnings(&);/'
printf "commit;\nEXIT\n" ) |
sqlplus -s myuser/myuser
I am trying to play with bash and arrays. But executing a sample script, I got an unexpected syntax error message: example.sh: 3: example.sh: Syntax error: "(" unexpected. And this is the script
#!/bin/bash
array=( one two three )
If I run the script with ./example.sh it works and no errors are displayed. But if I run sh example.sh I get the error message.
I thought that these two commands are the same:
sh example.sh
./example.sh
so ... what is the difference between the two?
When you launch it via ./example.sh then the command specified in the first line of the script is used to interpret the content. So your script executes in a bash, where such syntax is allowed for arrays.
When you launch it via sh example.sh then sh is the command that is used to interpret the content of the file. sh is the original Unix shell (aka Bourne shell) and this shell is a little more rude than bash (Bourne again shell). You don't have such arrays. Note that in sh the first line of your script is just interpreted as a comment.
by using sh example.sh
- you are specifying what shell interpreter to use for that script. Example being "bash example.sh" instead of "sh example.sh" etc etc.
Running scripts this way disregards the "shebang (#!/bin/bash)" that you have specified inside of the script. Since you wrote a bash script but are trying to run it as just "sh", this is why it is failing
by using ./example.sh,
- You are specifying to run the script from your current directory. This will attempt to run the script in whatever shell you are currently in unless a shebang is specified. Since you have a "shebang" specified to run the script in bash... this is why it is working.
array_name=(value1 ... valuen)
This is how to initializes an array in bash only. When you execute ./example.sh, the shebang line #!/bin/bash tells the system to use bash to execute.
However, when you execute sh example.sh, sh is used to execute. In many Unix systems (like Linux), sh is equivalent to bash. It seems sh is a different shell on your system.
I have some shell scripts which I run in my Linux/AIX machine with bash profile. Now my bash profile is going to be remove, and I will have Korn shell (ksh) or the C shell (csh). How to verify whether my scripts will run fine in Korn shell (ksh) or C shell (csh), even after bash shell is removed. Also, is there any differnce in commonly used commands between bash and other (ksh, csh). Is there command to check, which shell is getting used while running the shell script.
First of all, this is not a problem, the default shell of your account is irrelevant. As long as bash is installed on the machine, you can use it to run your code. Either add a shebang line as the first line of your script:
#!/usr/bin/env bash
Or, explicitly run the script with bash:
$ /bin/bash /path/to/script.sh
As for the differences, yes there are many. A script written for bash will not run in csh, their syntax is completely different. It might run on ksh but that will depend on your script. Not all features of the two shells are the same. For example:
$ cat test.sh
var="foo";
echo $var;
$ bash ./test.sh
foo
$ ksh ./test.sh
foo
$ csh ./test.sh
var=foo: Command not found.
var: Undefined variable.
As you can see above, var=foo runs correctly in ksh (which is part of the bourne shell family) but fails for csh. Basically, think of each shell as its own programming language. You wouldn't expect the python interpreter to be able to run a perl program, why do you expect one shell to be able to run a script written for another?
OP writes bash is going to be removed.
If you really cannot get bash installed. start each script with #!/bin/ksh and check for syntax problems:
ksh -n migrated_script
When you use bash/linux specific things you need to address them:
AIX will be "missing" flags on commands like find (changed last hour...) and ksh itself is also different.
Do not try csh, that is completely different.
I added the following command near the top of my shell script in order to record the script output to a file. This works with no problem when I run the script as my user, jsmith, however when the script is run as root in a crontab, I receive an error:
syntax error near unexpected token:
exec &> >(tee $LOG_PATH$TIMESTAMP.log)
I do have both $LOG_PATH and $TIMESTAMP correctly defined above the command as:
LOG_PATH="/home/jsmith/script/logs/"
TIMESTAMP="$(date -d "today" +"%Y-%m-%d-%H:%M")"
Any ideas? Thanks!
Usually, Linux feature multiple shells (sh, csh, dash, bash, etc.) which have subtle syntax differences. It is possible that you tested your script with bash, whereas crontabs are executed with dash.
I suggest you the following:
check what shell your script requires (looks at the first line)
tell cron to use that shell, i.e., set SHELL=/bin/my_shell at the beginning of your crontab (see the manpage for details).