Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
# This simple−minded cipher can be broken by an average 12−year old
#+ using only pencil and paper.
exit 0
tr variants
fold
fmt
The tr utility has two historic variants. The BSD version does not use brackets (tr a−z A−Z), but
the SysV one does (tr '[a−z]' '[A−Z]'). The GNU version of tr resembles the BSD one, so
quoting letter ranges within brackets is mandatory.
A filter that wraps lines of input to a specified width. This is especially useful with the −s option,
which breaks lines at word spaces (see Example 12−19 and Example A−2).
Simple−minded file formatter, used as a filter in a pipe to "wrap" long lines of text output.
Example 12−19. Formatted file listing.
#!/bin/bash
WIDTH=40
b=`ls /usr/local/bin`
# 40 columns wide.
# Get a file listing...
echo $b | fmt −w $WIDTH
# Could also have been done by
# echo $b | fold − −s −w $WIDTH
exit 0
See also Example 12−4.
A powerful alternative to fmt is Kamil Toman's par utility, available from
http://www.cs.berkeley.edu/~amc/Par/.
col
This deceptively named filter removes reverse line feeds from an input stream. It also attempts to
replace whitespace with equivalent tabs. The chief use of col is in filtering the output from certain text
processing utilities, such as groff and tbl.
column
Column formatter. This filter transforms list−type text output into a "pretty−printed" table by inserting
tabs at appropriate places.
Example 12−20. Using column to format a directory listing
#!/bin/bash
# This is a slight modification of the example file in the "column" man page.
Chapter 12. External Filters, Programs and Commands 174