I often see scripts with usage of options as in if [ -f some_file ] checks whether some_file is a file. I have a very vague understandings of flags, but can someone give me a good explanation? Others like -p, -s, I have no clue what they are and was unable to find good resources on them as a single google search doesn't yield any good result.
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Are you asking about "[]" command? That is basically called test command in Bash. Just lookup the man page of test.– VikybossFeb 14, 2016 at 5:33
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no, I am asking about options, a character follows by a "-"– 夢のの夢Feb 14, 2016 at 5:39
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You are asking for the option for test command. When you execute "man test" and look through it, you can see all the options(i.e, -f = FILE exists and is a regular file, -p FILE = exists and is a named pipe, etc.)– VikybossFeb 14, 2016 at 6:19
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Go to the official documentation gnu.org/software/bash/manual/…– cuonglmFeb 14, 2016 at 7:03
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basic examples and explanations can also be found here: cyberciti.biz/tips/…– xaaFeb 14, 2016 at 8:21
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2 Answers
Believe it or not, [ is actually another name for test command.
You can check the man page:
man test
test is a shell builtin too in most shells (and it gets precedence over the external one):
% type -a \[
[ is a shell builtin
[ is /usr/bin/[
% type -a test
test is a shell builtin
test is /usr/bin/test
In bash you can also see help test.
The best solution is the manual for bash, yes the simple man bash.
To find the exact entry in the manual, execute this command:
LESS=+/'^CONDITIONAL EXPRESSIONS' man bash
When working inside a bash shell, this also helps:
help test