CODEWITHSUNDEEP
bashsolaris
angie
angie

Reputation: 53

Will bash script pre-parse the syntax?

I am running bash script that needs to run different code for SunOs and Linux and I am getting the syntax error from the part of the code that not supposed to be true. I did not expect that since I thought that Bash works as interpreter.

The bash version on SunOS is 2.5 and on Linux is 4.1. The syntax it complains about is only supported from 3.1 version.

I tried to disable the newer code with "else" clause but it looks like it still pre-parses.

Also my script has ":" instead of "#! /bin/sh" as first line.

test.sh:

:
echo "`uname`"
if [ `uname` = "SunOS" ]
 then
    echo "do old stuff"
 else
    echo "new stuff"
    arr=($(grep "^X1" ../foo.txt | sed 's/.*=//'))
fi

The error is

> ./test.sh
SunOS
./test.sh: syntax error at line 8: `arr=' unexpected

If I comment error line then it will work fine:

:
echo "`uname`"
if [ `uname` = "SunOS" ]
 then
    echo "do old stuff"
 else
    echo "new stuff"
    #arr=($(grep "^X1" ../foo.txt | sed 's/.*=//'))
fi

The result is

> ./test.sh
SunOS
do old stuff

My question is how do I fix this syntax error without commenting? I have to have "if/else" to be able to run this script on different machines.

Upvotes: 2

Views: 165

Answers (2)

HardcoreHenry
HardcoreHenry

Reputation: 6387

You could stick the command in a temporary variable, and then execute the variable if your condition is true. I just ran the following on my system:

> if [ true ]; then echo hi; else [blah]=(--4); fi
-bash: syntax error near unexpected token `--4'

I get a syntax error as you describe. If I then do:

> if [ true ]; then echo hi; else var="[blah]=(--4)" && eval "${var}"; fi
hi

then it echos hi (no error). Finally if I do:

> if [ ]; then echo hi; else var="[blah]=(--4)" && eval "${var}"; fi
-bash: syntax error near unexpected token `--4'

Then it attempted to run the code, and generates an error based on trying to run the code.

Upvotes: 1

Gordon Davisson
Gordon Davisson

Reputation: 125758

That array syntax has been supported in bash since at least version 2; if you're getting errors there, it's because your script is not running under bash at all, but under some other shell. This probably has a lot to do with your script starting with : instead of a shebang line, meaning it's up to whatever runs the script to figure out what to run it with, with inconsistent results. I'd strongly recommend using a proper shebang line. If bash doesn't exist in a predictable location, you could use #!/usr/bin/env bash. If bash might not be in the PATH, you could use something like the script prologue here -- a #!/bin/sh shebang followed by commands to find and switch to bash.

As for the question about pre-parsing: yes, bash and other shells will parse all the way to the fi keyword before executing the if construct. They need to find the then, else, and fi keywords in order to figure out what they're going to execute and what they're going to skip, and in order to find those they have to parse their way to them.

Upvotes: 3

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