When are square brackets required in a Bash if statement?

bash if-statement square-bracket
Misha Moroshko picture Misha Moroshko · Jan 19, 2012 · Viewed 32.2k times · Source

Usually, I use square brackets in the if statement:

if [ "$name" = 'Bob' ]; then ...

But, when I check if grep succeeded I don't use the square brackets:

if grep -q "$text" $file ; then ...

When are the square brackets necessary in the if statement?

Answer

chepner picture chepner · Jan 19, 2012

The square brackets are a synonym for the test command. An if statement checks the exit status of a command in order to decide which branch to take. grep -q "$text" is a command, but "$name" = 'Bob' is not--it's just an expression. test is a command, which takes an expression and evaluates it:

if test "$name" = 'Bob'; then ...

Since square brackets are a synonym for the test command, you can then rewrite it as your original statement:

if [ "$name" = 'Bob' ]; then ...

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