Advanced Bash−Scripting Guide

[33] This is actually a script adapted from the Debian Linux distribution.
[34] The print queue is the group of jobs "waiting in line" to be printed.
[35] For an excellent overview of this topic, see Andy Vaught's article, Introduction to Named Pipes, in the
September, 1997 issue of Linux Journal.
[36] EBCDIC (pronounced "ebb−sid−ic") is an acronym for Extended Binary Coded Decimal Interchange
Code. This is an IBM data format no longer in much use. A bizarre application of the conv=ebcdic
option of dd is as a quick 'n easy, but not very secure text file encoder.
cat $file | dd conv=swab,ebcdic > $file_encrypted
# Encode (looks like gibberish).
# Might as well switch bytes (swab), too, for a little extra obscurity.
cat $file_encrypted | dd conv=swab,ascii > $file_plaintext
# Decode.
[37] A macro is a symbolic constant that expands into a command string or a set of operations on
parameters.
[38] This is the case on a Linux machine or a UNIX system with disk quotas.
[39] The userdel command will fail if the particular user being deleted is still logged on.
[40] For more detail on burning CDRs, see Alex Withers' article, Creating CDs, in the October, 1999 issue
of Linux Journal.
[41] The −c option to mke2fs also invokes a check for bad blocks.
[42] Operators of single−user Linux systems generally prefer something simpler for backups, such as tar.
[43] NAND is the logical "not−and" operator. Its effect is somewhat similar to subtraction.
[44] For purposes of command substitution, a command may be an external system command, an internal
scripting builtin, or even a script function.
[45] A file descriptor is simply a number that the operating system assigns to an open file to keep track of it.
Consider it a simplified version of a file pointer. It is analogous to a file handle in C.
[46] Using file descriptor 5 might cause problems. When Bash creates a child process, as with
exec, the child inherits fd 5 (see Chet Ramey's archived e−mail, SUBJECT: RE: File descriptor 5 is held
open). Best leave this particular fd alone.
[47] The simplest type of Regular Expression is a character string that retains its literal meaning, not
containing any metacharacters.
[48] Since sed, awk, and grep process single lines, there will usually not be a newline to match. In those
cases where there is a newline in a multiple line expression, the dot will match the newline.
#!/bin/bash
Advanced Bash−Scripting Guide
sed −e 'N;s/.*/[&]/'