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I want to learn more about the -n or -z option in IF condition,

I tried:

man if  
man condition

don't know where I can getto the the manpage of 'IF condition'.

terdon
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user956609
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    There is no `-n` nor `-z` option for `if`. If you think `-n` in `if [ -n something ]` belongs to the syntax of `if` then you're wrong. It belongs to the syntax of `[`. There is `man [` but note it describes a standalone `[` command. `[` in Bash is a builtin first, covered in `man bash`. In `if [[ -n something ]]` `-n` belongs to the syntax of `[[` which is a keyword in Bash. `[` and `[[` are similar but not equivalent. – Kamil Maciorowski Apr 23 '21 at 09:29
  • Adding to the information from the duplicate target: Bash usually gives you [three kinds of documentation](https://unix.stackexchange.com/a/159817/315749): the `help` builtin command you can use in interactive shells (`help if`, `help test`), the man page (`man bash`) and the Texinfo documentation (try `info bash if`, `info bash test`). Though AFAICT none of them makes it easy to get the relation between the `if` keyword/construct and the `-n`/`-z` `test` options at a glance. – fra-san Apr 23 '21 at 09:57
  • @fra-san They are documented in [section 6.4](https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html#Bash-Conditional-Expressions) of the Bash reference manual. – berndbausch Apr 23 '21 at 10:41

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