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EXPR(1L) EXPR(1L)
NNAAMMEE
expr - evaluate expressions
SSYYNNOOPPSSIISS
eexxpprr expression...
DDEESSCCRRIIPPTTIIOONN
This manual page documents the GNU version of eexxpprr. eexxpprr
evaluates an expression and writes the result on its stan-
dard output. Each token of the expression must be a sepa-
rate argument. Operands are either numbers or strings.
Strings are not quoted for eexxpprr, though you may need to
quote them to protect them from the shell. eexxpprr coerces
anything appearing in an operand position to an integer or
a string depending on the operation being applied to it.
The operators (in order of increasing precedence) are:
_| Yields its first argument if it is neither null nor
0, otherwise its second argument. This is the
usual `or' operation.
_& Yields its first argument if neither argument is
null or 0, otherwise 0.
_< _<_= _= _=_= _!_= _>_= _>
Compare their arguments and return 1 if the rela-
tion is true, 0 otherwise. (_=_= is a synonym for
_=.) eexxpprr tries to coerce both arguments to numbers
and do a numeric comparison; if it fails when try-
ing to coerce either argument it then does a lexi-
cographic comparison.
_+ _- Perform arithmetic operations. Both arguments are
coerced to numbers; an error occurs if this cannot
be done.
_* _/ _%
Perform arithmetic operations (`%' is the remainder
operation, as in C). Both arguments are coerced to
numbers; an error occurs if this cannot be done.
_: Perform pattern matching. Its arguments are
coerced to strings and the second one is considered
to be a regular expression, with a `^' implicitly
added at the beginning. The first argument is then
matched against this regular expression. If the
match succeeds and part of the string is enclosed
in `\(' and `\)', that part is the value of the _:
expression; otherwise an integer whose value is the
number of characters matched is returned. If the
match fails, the _: operator returns the null string
if `\(' and `\)' are used, otherwise 0. Only one
`\(' and `\)' pair can be used.
1
EXPR(1L) EXPR(1L)
In addition, the following keywords are recognized:
mmaattcchh _s_t_r_i_n_g _r_e_g_e_x
An alternative way to do pattern matching. This is
the same as ``_s_t_r_i_n_g :: _r_e_g_e_x''.
ssuubbssttrr _s_t_r_i_n_g _p_o_s_i_t_i_o_n _l_e_n_g_t_h
Return the substring of _s_t_r_i_n_g beginning at _p_o_s_i_-
_t_i_o_n with length at most _l_e_n_g_t_h. If either _p_o_s_i_-
_t_i_o_n or _l_e_n_g_t_h is negative or non-numeric, return a
null string.
iinnddeexx _s_t_r_i_n_g _c_h_a_r_a_c_t_e_r_-_c_l_a_s_s
Return the first position in _s_t_r_i_n_g where the first
character in _c_h_a_r_a_c_t_e_r_-_c_l_a_s_s was found. If no
character in _c_h_a_r_a_c_t_e_r_-_c_l_a_s_s is found in _s_t_r_i_n_g,
return 0.
lleennggtthh _s_t_r_i_n_g
Return the length of _s_t_r_i_n_g.
Parentheses are used for grouping in the usual manner.
The keywords cannot be used as strings.
EEXXAAMMPPLLEESS
To add 1 to the shell variable _a:
a=`expr $a + 1`
To find the filename part of the pathname stored in vari-
able _a, which may or may not contain `/':
expr $a : '.*/\(.*\)' '|' $a
Note the quoted shell metacharacters.
eexxpprr returns the following exit status:
0 if the expression is neither null nor 0,
1 if the expression is null or 0,
2 for invalid expressions.
2