Bash: Meaning of “[: too many arguments” error from if [] (square brackets)

Question

I couldn't find any one simple straightforward resource spelling out the meaning of and fix for the following BASH shell error, so I'm posting what I found after researching it.

The error:

-bash: [: too many arguments

Google-friendly version: bash open square bracket too many arguments.

Context: an if condition in single square brackets with a simple comparison operator like equals, greater than etc, for example:

VARIABLE=$(/some/command);
if [ $VARIABLE == 0 ]; then
  # some action
fi

Where is the code that produced this specific error? – Anderson Green Jun 17 '13 at 22:39 — Anderson Green, Jun 17 '13 at 22:39

score 90 · Accepted Answer

If your $VARIABLE is a string containing spaces or other special characters, and single square brackets are used (which is a shortcut for the test command), then the string may be split out into multiple words. Each of these is treated as a separate argument.

So that one variable is split out into many arguments.

The same will be true for any function call that puts down a string containing spaces or other special characters.

Easy fix

Wrap the variable output in double quotes, forcing it to stay as one string (therefore one argument). For example,

VARIABLE=$(/some/command);
if [ "$VARIABLE" == 0 ]; then
  # some action
fi

An alternate fix is to use double square brackets (which is a shortcut for the new test command).

This exists only in bash (and apparently korn and zsh) however, and so may not be compatible with default shells called by /bin/sh etc. This means on some systems, for example, it might work from the console but not from cron, depending on how everything is configured.

It would look like this:

VARIABLE=$(/some/command);
if [[ $VARIABLE == 0 ]]; then
  # some action
fi

http://stackoverflow.com/questions/13781216/bash-meaning-of-too-many-arguments-error-from-if-square-brackets

score 3 · Accepted Answer

echo "*file 2" | grep -o ^. prints *.

Since you have a command substitution outside double quotes, it undergoes globbing (a.k.a. wildcard matching a.k.a. filename generation) and word splitting. If the current directory is not empty, *expands to the list of files in the current directory. Each file becomes one token in the [ command, which is highly likely to be a syntax error.

The problem is that you didn't use double quotes around the command substitution. Always use double quotes around variable and command substitutions unless you have a good reason to omit them.

if [ "$(echo "*file 2" | grep -o ^.)" = '.' ]

See Why does my shell script choke on whitespace or other special characters? for a more detailed explanation.

Bash scripting

lunes, 11 de enero de 2016

bash checking vm

Bash: Meaning of “[: too many arguments

Bash: Meaning of “[: too many arguments” error from if [] (square brackets)

2 Answers

Easy fix

1 Answer

Enlaces

Entradas anteriores

Archivos