cheat sheets.

if [[ $foo = '' ]]; then
	print The parameter foo is empty
fi

# see also -z below

if [[ biriyana = b* ]]; then		
	print Word begins with a b
fi
# quote the term to avoid pattern matching (not regexp, btw)


# Numbers
if [[ $number -gt 3 ]]; then
if [[ $number -lt 3 ]]; then
if (( $number > 3 )); then
if (( 3 )); then	

# Files
if [[ file1 -nt file2 ]]; then		# newer than
if [[ file1 -ot file2 ]]; then		# older than
if [[ file1 -ef file2 ]]; then		# same file

# Variables
if [[ -z "$var is blah; test fails" ]]; then		# zero length?
if [[ -n "$var is blah; test passes" ]]; then		# non-zero length?

-a file
# true if file exists.

-b file
# true if file exists and is a block special file.

-c file
# # true if file exists and is a character special file.

-d file
# #true if file exists and is a directory.

-e file
# true if file exists.

-f file
# true if file exists and is a regular file.

-g file
# true if file exists and has its setgid bit set.

-h file
# true if file exists and is a symbolic link.

-k file
# true if file exists and has its sticky bit set.

-n string
# true if length of string is non-zero.

-o option
# true if option named option is on. option may be a single character, in which
case it is a single letter option name. (See 15.1 Specifying Options.)

-p file
# true if file exists and is a FIFO special file (named pipe).

-r file
# true if file exists and is readable by current process.

-s file
# true if file exists and has size greater than zero.

-t fd
# true if file descriptor number fd is open and associated with a terminal
device. (note: fd is not optional)

-u file
# true if file exists and has its setuid bit set.

-w file
# true if file exists and is writable by current process.

-x file
# true if file exists and is executable by current process. If file exists and
is a directory, then the current process has permission to search in the
directory.

-z string
# true if length of string is zero.

-L file
# true if file exists and is a symbolic link.

-O file
# true if file exists and is owned by the effective user ID of this process.

-G file
# true if file exists and its group matches the effective group ID of this
process.

-S file
# true if file exists and is a socket.

-N file
# true if file exists and its access time is not newer than its modification
time.

file1 -nt file2
# true if file1 exists and is newer than file2.

file1 -ot file2
# true if file1 exists and is older than file2.

file1 -ef file2
# true if file1 and file2 exist and refer to the same file.

string = pattern
string == pattern
# true if string matches pattern. The `==' form is the preferred one. The `='
form is for backward compatibility and should be considered obsolete.

string != pattern
# true if string does not match pattern.

string1 < string2
# true if string1 comes before string2 based on ASCII value of their characters.

string1 > string2
# true if string1 comes after string2 based on ASCII value of their characters.

exp1 -eq exp2
# true if exp1 is numerically equal to exp2.

exp1 -ne exp2
# true if exp1 is numerically not equal to exp2.

exp1 -lt exp2
# true if exp1 is numerically less than exp2.

exp1 -gt exp2
# true if exp1 is numerically greater than exp2.

exp1 -le exp2
# true if exp1 is numerically less than or equal to exp2.

exp1 -ge exp2
# true if exp1 is numerically greater than or equal to exp2.

( exp )
# true if exp is true.

! exp
# true if exp is false.

exp1 && exp2
# true if exp1 and exp2 are both true.

exp1 || exp2
# true if either exp1 or exp2 is true.


# NB Arrays get treated as words separated by spaces.

TBC