Linux Shell Scripting Cookbook - Third Edition

Squeezing characters with tr

The tr command can perform many text-processing tasks. For example, it can remove multiple occurrences of a character in a string. The basic form for this is as follows:

tr -s '[set of characters to be squeezed]' 

If you commonly put two spaces after a period, you'll need to remove extra spaces without removing duplicated letters:

$ echo "GNU is       not     UNIX.  Recursive   right ?" | tr -s ' '
GNU is not UNIX. Recursive right ?

The tr command can also be used to get rid of extra newlines:

$ cat multi_blanks.txt | tr -s '\n'
line 1
line 2
line 3
line 4

In the preceding usage of tr, it removes the extra '\n' characters. Let's use tr in a tricky way to add a given list of numbers from a file, as follows:

$ cat sum.txt ...