无缘无故回显打印工作目录文件名

Question

why echo printing the files names ?

sinks_index=`pacmd list-sinks | grep "index:"`

for i in $sinks_index
    do  
        echo $i
    done

gives this output

audio_name_switcher.sh
audio.py
audio.sh
switch_audio.sh
index:
1
index:
2
index:
3

but running pacmd list-sinks | grep "index:" pacmd list-sinks | grep "index:" in the shell gives * index: 1 index: 2 index: 3

Answer 1

pacmd returns * pattern.

In for ... in ...; do ... done for ... in ...; do ... done loop, the list pattern contains * without any protection.

So, bash replace * by all files found in current directory.

It's the glob functionality.

You could temporary deactivate glob with GLOBIGNORE variable (see man bash ):

#! /bin/bash
sinks_index='* index: 1 index: 2 index: 3'

GLOBIGNORE="*"
echo "With GLOBIGNORE"
for i in $sinks_index
    do
        echo "UNSET GLOB: " $i
        unset GLOBIGNORE
        echo "  SET GLOB: " $i
        echo "  SET GLOB: $i"
    done
unset GLOBIGNORE

Reactivate global in and after loop.

• In: it may be necessary for other stuff;
• After: if your list is empty, the execution do not enter in the loop.

Note about $i and "$i" after reactivate glob in the loop:

• The protection with "..." stop glob for bash echo command but do not stop ${...} interpretation.

Answer 2

You should be using an array for sinks_index , not a scalar:

sinks_index=( $(pacmd list-sinks | grep "index:") )

for i in "${sinks_index[@]}"
    do  
        echo "$i"
    done

The above will solve the problem you asked about but is making several assumptions about the output of pacmd list-sinks so consider that a starting point but you may need a more robust or slightly different solution depending on that output and what you actually want to do with it.

Copy/paste your shell scripts into http://shellcheck.net til you get familiar with shell.