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The wc command stands for "word count". It reads one or more input files and, by default, writes the number of newline characters, words and bytes contained in each input file to the standard output. Most often used as the last stage of pipes like ps -e | wc -l
If more than one input file is specified, a line of cumulative count(s) for each of specified files as well as is total count for all files is printed.
3 rarme.bat 11 robots.txt 334 safary.shtml 2993 strange_files.txt 1 today.lst 18 topbooks.htm 37 topupdates.htm 38 topvisited.htm 124 truncate2.pl 15 update.bat 1 xcopy_sp.sh 18791 total
When an option is specified, wc only reports the information requested by that option. Option -w counts words. Historically, the wc defines a word as a ``maximal string of characters delimited by <space>, <tab> or <newline> characters''. Such a definition creates problem with non-printable characters. Most modern implementations defines a ``word'' in terms of the isspace(3) function, as required by IEEE Std1003.2-1992 (``POSIX.2'').
The default behavior presuppose options -clw having been specified.
If no option is specified, the default is -lwc (counts lines, words, and bytes.). The -c and -m options are mutually exclusive.
who | wc -l
counts the number of users logged
ps -e | wc -l
counts the number of processes
ls -l | grep ^d | wc -l # finds the number of subdirectories in the current directory.
wc -l /etc/passwd
tells you the number of lines (accounts) in the /etc/passwd file.
wc -w readme.txt
counts the number of words in the file named readme.txt
Useless Use of wc -lThis is my personal favorite. There is actually a whole class of "Useless Use of (something) | grep (something) | (something)" problems but this one usually manifests itself in scripts riddled by useless backticks and pretzel logic.
Anything that looks likecan usually be rewritten like something along the lines ofsomething | grep '..*' | wc -lor even (if all we want to do is check whether something produced any non-empty output lines)something | grep -c . # Notice that . is better than '..*'(or grep -q if your grep has that).something | grep . >/dev/null && ...
If something is reasonably coded, it might even already be setting its exit code to tell you whether it succeeded in doing what you asked it to do; in that case, all you have to check is the exit code:something && ...
I used to have a really wretched example of clueless code (which I had written up completely on my own, to protect the innocent) which I've moved to a separate page and annotated a little bit. It expands on the above and also has a bit about useless use of backticks (q.v.)
wc- display a count of lines, words and characters in a file
wc [-c| -m| -C] [-lw] [file...]
The wc utility reads one or more input files and, by default, writes the number of newline characters, words and bytes contained in each input file to the standard output.
The utility also writes a total count for all named files, if more than one input file is specified.
The following options are supported:
Same as -m.
Count words delimited by white space characters or new line characters. Delimiting characters are Extended Unix Code (EUC) characters from any code set defined by iswspace().
If no option is specified the default is -lwc (count lines, words, and bytes.)
The following operand is supported:
A path name of an input file. If no file operands are specified, the standard input will be used.
See largefile(5) for the description of the behavior of wc when encountering files greater than or equal to 2 Gbyte ( 231 bytes).
See environ(5) for descriptions of the following environment variables that affect the execution of wc: LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following exit values are returned:
An error occurred.
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