if语句中的fish shell -eq和-a

Question

I was reading the git.fish completion script (/usr/local/Cellar/fish/2.1.2/share/fish/completions) for fish shell and I ran into some problems with understanding what the syntax means.

In the block,

function __fish_git_needs_command
  set cmd (commandline -opc)
  if [ (count $cmd) -eq 1 -a $cmd[1] = 'git' ]
    return 0
  end
  return 1
end

I understand that cmd is set as commandline -opc . But in the next statement (count $cmd) -eq 1 -a $cmd[1] = 'git' , what do -eq and -a mean?

I am new to fish shell and I am trying to understand the syntax by trying to write my own completion script for a program. Help would be greatly appreciated.

Thank you.

Answer 1

In fact -eq and -a are not part of fish syntax. They are ordinary arguments!

if [ (count $cmd) -eq 1 -a $cmd[1] = 'git' ]

The opening square bracket here is actually a command, like cat or grep. You really do have a file /bin/[ . It may be easier to understand via the test command, which is the same thing:

if test (count $cmd) -eq 1 -a $cmd[1] = 'git'

Now it's easy to see that -eq and -a are just ordinary arguments being passed to test , with no syntactic significance to fish.

test has its own little language like awk or sed. See man test to learn about it.

Answer 2

The -eq is an integer comparison function .

The -a is a logical and .

So the logical equivalent would be something like:

if [ (count $cmd) == 1 && $cmd[1] == 'git' ]

(in Java pseudo-syntax).

Background

The reason why -eq is used is because a shell normally works with text processing only. As a result numbers are stored in "strings". Sometimes two numbers are equivalent, but not string-equivalent. For instance the following example:

if [ "01" -eq "1" ]
then
    echo "integer equal"
fi
if [ "01" = "1" ]
then
    echo "string equal"
fi

Will only print integer equal .

Answer 3

From the Fish documentation :

• NUM1 -eq NUM2 returns true if NUM1 and NUM2 are numerically equal.
• COND1 -a COND2 returns true if both COND1 and COND2 are true.

It tests that (count $cmd) = 1 and that $cmd[1] = 'git' .
( = here being equality, not an assignment).