- wc:-
- This counts words lines and
characters. To count the number of files in a directory, try
ls | wc -l
- grep:-
- `
grep Kwan /etc/passwd'
prints all lines in /etc/passwd that include `Kwan'. The
return value indicates whether any such lines have been found.
- sed:-
- a stream editor. Doing
ls | sed s/a/o/g will
produce a listing where all the 'a' characters become 'o'. Numerous
tricks and tutorials are available from the
Handy one-liners for SED
file.
- basename:-
- Strips the directory and (optionally) suffix from
a filename.
- tr:-
- Translates one set of characters to another set. For example, try
echo "date" | tr d l
The following does case conversion
echo LaTeX | tr '[:upper:]' '[:lower:]'
You can also use it as follows, ``capturing"
the output in a variable
old="LaTeX"
new=$(echo $old | tr '[:upper:]' '[:lower:]')
- test:-
- This program can be
used to check the existence of a file and its permissions, or to
compare numbers and strings. Note that `
if [ -f data3 ]'
is equivalent to ` if test -f data3'; both check for a
file's existence, but the [...] construction is faster - it's a
builtin. Note that you need spaces around the square brackets.
Some examples,
if [ $LOGNAME = tpl ] # Did the user log in as tpl?
if [ $num -eq 6 ] # Is the value of num 6?
if [ $(hostname) = tw000 ] # Does hostname produce `tw000'?
# i.e. is that the machine name?
- sort:-
- `
ls -l | sort -nr +4'
lists files sorted according to what's in column 4 of ls -l's output (their size, usually).
- cut:-
- Extracts characters or fields from lines.
cut -f1 -d':' < /etc/passwd prints all the uid's in the passwd
file. The following code shows a way to extract parts of a filename.
filename=/tmp/var/program.cc
b=$(basename $filename)
prefix=$(echo $b | cut -d. -f 1)
suffix=$(echo $b | cut -d. -f 2)
- find:-
- finds files in and below directories according to their
name, age, size, etc.
