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There's a short section in my .bashrc file that I don't understand and I'd like to ask what it means and some syntax explanation.

# Alias definitions.
# You may want to put all your additions into a separate file like
# ~/.bash_aliases, instead of adding them here directly.
# See /usr/share/doc/bash-doc/examples in the bash-doc package.

if [ -f ~/.bash_aliases ]; then
    . ~/.bash_aliases
fi

I understand of course that # makes every line a comment.

Can you please explain to me the if ... then statement. What -f means?

Why there are [] in the first line of the code?

Why there's ; after the [ -f ~/.bash_aliases ]?

Why the second line of the code starts with a . and what it actually means, this whole second line. I know that .bash_aliases is a file containing bash_aliases in Linux, but this second line I don't understand.

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    Related: What does -f mean in an if statement in a bash script? Commented Mar 25, 2022 at 22:50
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    Does this answer your question? What does -f mean in an if statement in a bash script? Commented Mar 26, 2022 at 12:38
  • It almost feels like we have duplicate comments suggesting that this question is a duplicate? Can that be right? On a more serious note, that question’s answer does not explain the ., so it is not a duplicate. Commented Mar 26, 2022 at 12:51
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    @Quasímodo I assume that before doing any of that, we should head to the proposed duplicate and cast some downvotes and close votes there. It currently has a score of 9 and two answers. One answer is dodgy, but even that answer has a score of 10. There seem to be a lot of inconsistencies here. Commented Mar 27, 2022 at 6:31

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  1. Can you please explain to me the if ... then statement.

    In plain English: If there is a file named .bash_aliases in your home directory, source it.

  2. What -f means?:

    Test if a file exists and is a regular file (not a directory etc.), or a symbolic link to a regular file.

  3. Why there are [] in the first line of the code?

    That's the shell command for performing a test. An alternative way is if test -f .bash_aliases; then

  4. Why there's ; after the [ -f ~/.bash_aliases ]?

    The semicolon is a command separator in bash. You need it here to end the test command and allow the then block to start on the same line.

    Alternatively, you can avoid using the ; as a separator and explicitly split the commands using a line break.

    if [ -f ~/.bash_aliases ]
then

  5. Why the second line of the code starts with a . and what it actually means

    That's the name of a command to execute. The . (dot) command is a shell builtin command that sources a file. With the reasonable assumption that bash will execute the file .bashrc, the more readable but non-POSIX command source may be used instead of .

    source ~/.bash_aliases

Be aware that some shells, for example dash and some variants of ksh, do not support source though.

You might want to read bash documentation.

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    [ is a program. You will find it in /bin/[. Some shells may optimise by handling it internally instead of calling the actual executable. Commented Mar 26, 2022 at 12:36
  • @OrangeDog There is no guarantee that the shell’s built-in [ will behave the same way as the external command in /bin/[. Indeed, my Debian 10 system’s man page for [ says: “Please refer to your shell's documentation for details about the options it supports.” Commented Mar 26, 2022 at 12:55
  • @BrianDrake they are guaranteed to behave in exactly the same way. Especially if the docs for one refer you to the other. Commented Mar 26, 2022 at 19:16
  • @OrangeDog Although an identical behavior is expected in most cases, there is not guarantee that both always behave the same way. For example errors message might vary. Commented Mar 26, 2022 at 21:51
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    @OrangeDog The [ man page I cited gives a complete description of the external [ command, before stating that the shell may have its own version and referring the user to the shell’s documentation. The bash man page also has a complete description of bash’s implementation. A cursory look suggests that there are at least two differences: only bash’s implementation supports -a as a synonym for -e, and only the external command supports -l for the length of a string. Commented Mar 27, 2022 at 6:41

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