NAME

ch - make changes in text files


SYNOPSIS

ch [-ax] [expr ...] fromexpr [toexpr]


DESCRIPTION

Ch
copies each line of the standard input to the standard output, globally
substituting the text pattern "toexpr" for "fromexpr" on each line that
satisfies matching criteria defined by the leading expressions "expr" and
the switches. (A text pattern is a subset of a "regular expression"--see
the "ed" writeup for a complete description.)  Three possible courses of
action are taken depending upon the number of text patterns(n) found in
the command line:



n=1  The text pattern is assumed to be "fromexpr" with a null "toexpr";
it is equivalent to the ed command

g/fromexpr/s///g

n=2  The first text pattern is "fromexpr", the second is "toexpr"; it
is equivalent to the ed command

g/fromexpr/s//toexpr/g

n>=3 The (n-1)th pattern is "fromexpr", the nth is "toexpr" and patterns
1...n-2 are used to determine the lines upon which to perform the
substitution.  The default is that any line which matches any one of
the n-2 leading expressions are eligible for substitution.  If the -a
flag is specified, only lines which match all n-2 leading expressions in
any order are eligible.  If the -x flag is specified, all lines which
don't satisfy the above criteria are eligible. (See the writeup on find
for more information.)  In particular, if n=3,

ch expr from to

is equivalent to the ed command

g/expr/s/from/to/g

ch -x expr from to

is equivalent to the ed command

x/expr/s/from/to/g


The substitution string "toexpr" may be a string of replacement
characters, null to effect a deletion, or it may include the special
"ditto" character "&" to put back the "fromexpr" string and thus
effect an insertion.  If a deletion is desired with the multiple
leading tag expressions, a "toexpr" of "" -i.e. quotes around an
empty string may be used.

A text pattern consists of the following elements:


c         literal character
?         any character except newline
%         beginning of line
$         end of line (null string before newline)
[...]     character class (any one of these characters)
[!...]    negated character class (all but these characters)
*         closure (zero or more occurrences of previous pattern)
{...}     'tagged' (marked) pattern
@c        escaped character (e.g., @%, @[, @*)


Any special meaning of characters in a text pattern is lost when
escaped, inside [...], or for:


%         not at beginning
$         not at end
*         at beginning


A character class consists of zero or more of the following
elements, surrounded by [ and ]:


c         literal character
a-b       range of characters (digits, lower or upper case)
!         negated character class if at beginning
@c        escaped character (@! @- @@ @])


Special meaning of characters in a character class is lost when
escaped or for


!         not at beginning
-         at beginning or end


An escape sequence consists of the character @ followed by a single
character:


@n        newline
@t        tab
@c        c (including @@)


For a complete description, see "Software Tools" pages 135-154.
Care should be taken when using the characters % $ [ ] { } ! * @ and
any shell characters
in the text pattern. It is often necessary to enclose the
entire substitution pattern in quotes.


FILES

None


SEE ALSO

sedit, find, tr, ed, the UNIX tool GRES


DIAGNOSTICS

An error message is printed if the pattern given is illegal.


AUTHORS

Original from Kernighan and Plauger's "Software Tools", with
modifications by Joe Sventek (Lawrence Berkeley Laboratory)


BUGS/DEFICIENCIES

A minus sign(dash[-]) may not start an expression.