Lecture #9 – Utilities

• Order of command line expansion

1. Brace Expansion { }
2. Tilde Expansion ~
3. Parameter Expansion $1 $2 $3
4. Variable Expansion $ABC $HOME
5. Command Substitution `pwd` or ($pwd)
6. Arithmetic Expansion $[ expression ]
7. Word Splitting uses IFS variable
8. Pathname Expansion * ? [ ]

Note: the command in #5 is executed before any expansion and as a separate command line.

Note: Variable assignment occurs before pathname expansion.

• wc – word count

wc [-c] [-w][-l] [filenames]

counts the number of lines, words and characters

without any filenames, wc reads input from stdin.

Note: the following two commands produce slightly different output.

$ wc –l cars

14 cars

$ cat cars | wc –l

14

• readonly – marks a shell variable as un-changeable

$ A=test

$ readonly A

$ A=new

-bash: A: readonly variableq

readonly [filenames]

readonly without any parameters displays a list of readonly variables.

• umask – change the default file-creation permission mask.

umask <permission mask>

Each bit TURNS OFF the permission for all files created after being set.

umask 000 – Leaves all bits unchanged, files are created with 666 permissions.

umask 066 – Turns off permissions for groups and others on new files.

umask 022 – Turns off Write permission for groups and others on new files.

• Find – find files

find <dir> options

Very flexible utility for finding files in a directory tree.

Many options, see page 600 for more info.

List all files starting in the current directory and working down, named “a.out”.

find . –name a.out –print

List all file under /usr/bin modified less than 300 days ago.

find /usr/bin –mtime -300 –print

Normally, options are combined as a AND, but can be change to an OR with the “-o” option.

find . –name a.out –print –o –name core –print

Find can also execute a command on each file it finds with the –exec option.

The command must end with a “;” and {} is replaced with the filename.

find /tmp –mtime 3 –exec ls –l \{\}\ ; list all temp file older than 3 days.

• cpio – Copy In and Out

Stores and retrieves files in an archive format.

ALSO, useful for copying an entire directory and all subdirectories.

cpio –o reads stdin for a list of filenames, and combines these files into a single archive that is written to stdout.

cpio –i reads a file from stdin that it previously created with cpio –o. cpio will then selectively extract files from the archive.

cpio –p read stdin for a list of filenames, and passes these files to a directory given as an argument to the command.

ls *.c | cpio –o > source.archive <-- creates a backup of C source files

cpio –i < source.archive <-- restores the archive

find cs390 –print | cpio –p uah <-- copies directory cs390 to uah/cs390

• set – override the command line variables

The ‘set’ command takes the following parameters and assigns them to $1, $2, $3, etc.

Example:

$ wc carsort3

31 121 719 carsort3

$ set `wc carsort3`

$ echo $1

31

$ echo $2

121

$ echo $3

719