Take Command

wc--Word Count

A simple command with a lot of uses.

by Alexandre Valente Sousa

The wc (word count) command is a very simple utility found in all Unix variants. Its purpose is counting the number of lines, words and characters of text files. If multiple files are specified, wc produces a count for each file, plus totals for all files.

When used without options wc prints the number of lines, words and characters, in that order. A word is a sequence of one or more characters delimited by whitespace. If we want fewer than the three counts, we use options to select what is to be printed: -l to print lines, -w to print words and -c to print characters. The GNU version of wc found in Linux systems also supports the long options format: --chars (or --bytes), --words, --lines.

When I applied wc to an earlier version of the LaTeX source file with this text, I received the following information from wc:

wc wc.tex
     98     760    4269 wc.tex

This line means that the file had 98 lines, 760 words and 4269 characters (bytes). Actually, I seldom use wc alone. Due to its simplicity wc is mostly useful when used in combination with other Linux commands.

If we use a file system other than Linux (or Unix), namely DOS, there is an ambiguity due to a line break being a combination of a carriage return and a line feed. Should -c count a line break as two characters or only one? The POSIX.2 standard dictates that -c actually counts bytes, not characters, and it provides the -m option to count characters. This option cannot be used together with -c, and for that matter, GNU wc does not support -m. If we desperately need it, we can always subtract the line count from the byte count to obtain the char count of a DOS file. Here are two different ways to achieve this:

wc /dosc/autoexec.bat | awk '{print $3-$1}'
tr -d '\015' < /dosc/autoexec.bat | wc -c

The first solution uses awk to subtract the first field (the line count) from the third field (the byte count). The second solution uses tr to delete the carriage returns (char 15 in octal) from the input before feeding it to wc.

Recently I used a CD-ROM writer that was connected to a machine that was slightly sick. Now and then a block of 32 consecutive bytes got corrupted while copying amongst different hard disk partitions. This caused quite a few CD-ROM backups to be damaged. Sometimes the damage affected a large file, and in this case, it was cheaper to keep the bad file and add a small patch file to the next backup. To decide whether we should make a new full backup of a corrupted file or just make a differential patch, we used the cmp command to detect the differences, followed by wc to count them:.

cmp -l /original/foo /cdrom/foo | wc -l

The -l option to cmp provides a full listing of the differences, one per line, instead of stopping on the first difference. Thus, the above command outputs the number of bytes that are wrong.

If we want to count how many words are in line 70 of file foo.txt then we use:

head -70 foo.txt | tail -1 | wc -w

Here, the command head -70 outputs the first 70 lines of the file, the command tail -1 (i.e., the number 1) outputs the last line of its input, which happens to be line 70 of foo.txt, and wc counts how many words are in that line.

If our boss presses us to include in our monthly project report a count of the number of lines of code produced, then we can do it like this:

wc -l */*.[ch] | tail -1 | awk '{print $1}'

This assumes that all our code is in files with extension .h or .c, and that these files live in subdirectories one level deep from our current directory. If file depth is arbitrary, we use the following:

wc -l `find . -name "*.[ch]" -print` | \
         tail -1 | awk '{print $1}'

Notice the use of back quotes in the find command line, and forward (normal) quotes in the awk command. The command find . -name "*.[ch]" -print outputs the *.c and *.h files located below the current directory, one per line. The back quotes cause that command to be executed, and then replace each newline in the command's output with a blank, and pass that output to the wc command line.

If in good GNU style you mark all current bugs and dirty hacks in your source code with the word FIXME, then you can see how much urgent work is pending by typing:

grep FIXME *.c | wc -l

The grep outputs all lines that have a FIXME, and then we just have to count them.

As you can see there is nothing special about the wc command; however, half of my shell scripts would stop working if that command was not available.

Alexandre (avs@daimi.aau.dk) is from Porto, Denmark, but has been in Aarhus for his PhD, just delivered--something to do with literate programming and stuff. He is ashamed to confess that his first Linux was 1.02, but he is playing catch up. He claims to have brainwashed his significant other, Renata, and now she is even more sanguine about Linux. Now they are threatening to capture the mind and soul of their innocent 9 year old daughter Maria. She has a Mac but with the release of MkLinux she is no longer safe. Root password at 9? Cool.