Classic Shell Scripting

Reformatting Paragraphs

Most powerful text editors provide commands that make it easy to reformat paragraphs by changing line breaks so that lines do not exceed a width that is comfortable for a human to read; we used such commands a lot in writing this book. Sometimes you need to do this to a data stream in a shell script, or inside an editor that lacks a reformatting command but does have a shell escape. In this case, fmt is what you need. Although POSIX makes no mention of fmt, you can find it on every current flavor of Unix; if you have an older system that lacks fmt, simply install the GNU coreutils package.

Although some implementations of fmt have more options, only two find frequent use: -s means split long lines only, but do not join short lines to make longer ones, and -w n sets the output line width to n characters (default: usually about 75 or so). Here are some examples with chunks of a spelling dictionary that has just one word per line:

$ sed -n -e 9991,10010p /usr/dict/words | fmt        
            Reformat 20 dictionary words
Graff graft graham grail grain grainy grammar grammarian grammatic
granary grand grandchild grandchildren granddaughter grandeur grandfather
grandiloquent grandiose grandma grandmother

$ sed -n -e 9995,10004p /usr/dict/words | fmt -w 30  
            Reformat 10 words into short lines
grain grainy grammar
grammarian grammatic
granary grand grandchild
grandchildren granddaughter

If your system does not have /usr/dict/words, then it probably has an equivalent file named