Save the output of a command to a variable

Question

The command mid3v2 -l someFile.mp3 gives the following output for a file with name someFile.mp3 in mp3-format:

IDv2 tag info for someFile.mp3
APIC=cover front,  (image/jpg, 52016 bytes)
TALB=someAlbumName
TCON=amusicGenre
TDRC=2000
TIT2=songname
TPE1=singer
TPE2=singer
TRCK=1

I would like to store the value of TPE1 to a variable t for further processing. How can i do this?

Answer 1

There are many ways to answer this question.
The first step is to understand that the output of a command could be received by other commands via a pipe, or, could be captured in a variable:

cmd | next command ... etc
var=$(cmd)

The process to select a line and further select what is after the sign = is called "text processing" and the shell is not well suited to do it.

A common way to do it may be sed:

 $ mid3v2 -l someFile.mp3 | sed -En 's/^TPE1=(.*)$/\1/p'
 Singer

And capture the result to a variable:

$ t=$(mid3v2 -l someFile.mp3 | sed -En 's/^TPE1=(.*)$/\1/p')
$ echo "$t"
Singer

There is no simple equivalent inside a simple shell. On higher shells (ksh,bash,zsh) it is possible to use regex. Which shell do you use?

Answer 2

Given your shell provides "process substitution", you might try "sourcing" the result:

. <(mid3v2 -l someFile.mp3 | grep -o "[^ ]*=[^ ]*")
t=$TPE1