Quotes within Bash Shell variable do not work, why?

Question

#!/bin/sh
LOG='log --pretty=format:"%h - %an, %ar : %s"'

git $LOG

I expect this to output an actual git log in the specified format. However, all I get is a fatal argument error.

I have also tried the options below, and they also do not work:

LOG="log --pretty=format:\"%h - %an, %ar : %s\""
LOG='log --pretty=format:\"%h - %an, %ar : %s\"'

However, strangely the script below DOES work, and I don't understand why:

LOG='--pretty=format:"%h - %an, %ar : %s"'
git log "$LOG"

It has been argued that shell is considering the variable to be only one argument, however the following works fine:

LOG1LINE='log --pretty=oneline'
git $LOG1LINE

I'm trying to put a command in a variable, but the complex cases always fail — glenn jackman
– glenn jackman, Commented Jul 23, 2013 at 17:40

onlywei · Accepted Answer · 2013-07-23 17:58:41Z

4

Here is one way to overcome this problem. Using bash arrays:

#!/bin/bash
#It's important to use bash instead of sh for this to work

LOG=(log --pretty=format:"%h - %an, %ar : %s")
git "${LOG[@]}"

edited Jul 23, 2013 at 17:58

onlywei

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answered Jul 23, 2013 at 15:53

anubhava

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7 Comments

onlywei Over a year ago

I get "Syntax error: "(" unexpected" when I try to declare my array. I get it even if I use declare -a LOG=(b).

anubhava Over a year ago

Are you sure you're using bash?

onlywei Over a year ago

I'm using the default terminal that comes with Ubuntu. How can I check for sure?

anubhava Over a year ago

Run this: echo $SHELL

onlywei Over a year ago

echo $SHELL results in: /bin/bash

|

Taymon · Accepted Answer · 2013-07-23 15:39:14Z

2

This is a product of how the shell handles arguments.

The first thing the shell does is substitute variables. Quotes that were used in the variable definition are not preserved here. Then it chunks them into arguments, based on either quotes or, if these are not present, word boundaries. Quotes that were quoted when they were first used are escaped at that time, and consequently cannot define word boundaries.

Consequently, the arguments passed to git in your first example are:

log
--pretty=format:"%h
-
%an,
%ar
:
%s"

In the later example, the arguments passed to git are:

log
--pretty=format:"%h - %an, %ar : %s"

edited Jul 23, 2013 at 15:39

answered Jul 23, 2013 at 15:21

Taymon

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2 Comments

onlywei Over a year ago

Is there any way to preserve the quotes?

Gordon Davisson Over a year ago

@onlywei: Not really. The shell parses (& removes) quotes before replacing variable values, so by the time any quotes in the variable appear, it's too late for them to do any good. Solution: use an array instead (see anubhava's answer).

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