Linux Commands

grep

grep -Rsl PATTERN [FILE]            # Recursive, no error output, only list filename
grep BASIC-REG-EXP-PATTERN [FILE]   # Use classic regexp (like "dma\|DMA")
egrep EXT-REG-EXP-PATTERN [FILE]    # Same as grep -E. Use extended regexp (like "dma|DMA")
fgrep FIXED-STRINGS-REG-EXP [FILE]  # Same as grep -F. Pattern is a list of strings to match.
grep -n PATTERN [FILE]              # Print matched line numbers.
grep -- "-s" [FILE]                 # Search for text "-s"

sed

sed [OPTION]... {script-only-if-no-other-script} [input-file]...
sed -n                              # Silent - suppress automatic printing of pattern space
sed -r                              # Use extended regular expression

Regular expressions

The information below is only illustrative. See e.g. Wikipedia page for reference information. The list below is actually for extended regular expressions, which can be obtained in sed using option -r (sed -r).

Regexp	Description
.	Match any character
gray|grey	Match gray or grey
gr(a|e)y	Match gray or grey
gr[ae]y	Match gray or grey
file[^0-2]	Match file3 or file4, but not file0, file1, file2.
colou?r	(zero or one) - Match Color or Colour.
ab*c	(zero or more) - Match ac, abc, abbc, ....
ab+c	(one or more) - Match abc, abbc, abbbc, ....
a{3,5}	(at least m and not more than n times) - Match aaa, aaaa, aaaaa.
^on single line$	(start and end of line) - Match on single line on a single line.

When using standard (non-extended) regular expression, some special meta-characters (like the parenthesis ( ), or braces { }) must be quoted with backslash \.

Miscellaneous

htop

an improved top command (http://htop.sourceforge.net/index.php)

strace

trace system calls and signals