外壳中的$（wc -l $ title_file）集合是什么意思？

Question

These days.i'm learning the shell script for fun.When i read the manual's example like:

set $(wc -l $title_file)
  num_titles=$1
  set $(wc -l $tracks_file)
  num_tracks=$1

And i have the brief understanding that the command,set,specify the $1 and set the value of $1 to the num_titles. But,i have no idea why use -l as the option for the command,set.And by the way,would any guy can explain the whole story of it?thx

Answer 1

the -l switch is counting the number of lines in the specified file(s) in your case, it is counting the number of lines in the titles file and setting it to the num_titles variable (and counting the number of lines in the file specified by the tracks_file variable and setting the value to num_track variable)

you can simply try wc -l on the command line to see the value it prints out

Answer 2

Firstly set sets an environment variable. Using the syntax set var = value or set var [n] = word as per its manpage , to view the manpage type man set .

In this case set is using the second syntax to make $1 = $(wc -1 $titlefile) and then setting num_titles to $1 as a regular variablle because of the syntax used.

wc is the wordcount command, and displays lines, characters and words in a file.

wc -l tells wc to count by line as per the wc manpage, to view the manpage type man wc .

See the Linux Shell Scripting Tutorial A Beginner's handbook and the Advanced Bash-Scripting Guide for further references.