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<<TOC>>
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*** Title: Regsub -all, Match Line, and Replace, Working on a Text File V2 ***
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[gold] Note to clean up crew. Checking end of line issues here from laptop PC editor. If one sees a syntax error or brace typo error, go ahead and change. My eyes are bad on these tiny fonts.
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***Find a text in a line and replace the next line***
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[gold] 3/26/2024. Found example code for [regsub] on [Ask, and it shall be given # 11].
Seemed a useful lesson and example code on regsub and replace, if category links and Wiki page references were added to find same in the Wiki stacks.
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***Question: Working on a Text File V2 ***
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tclamateur : I want to find a text in a line and replace the contents of the next line with a new string. I tried regsub, but it is only matching the first line. I don't know how to go to the next line.
eg:
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======
line 5> this is line 5.
line 6> apple
with
line 5> this is line 5.
line 6> banana
======
Thanks
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*** First Example ***
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[AMG]: [[[regsub]]] has the `-all` option to replace every occurrence, not just the first.
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proc replace {match replacement text} {
# Backslash-quote special characters in match and replacement so they will
# be interpreted as literal strings.
regsub -all {[][*+?{}()<>|.^$]} $match {\\&} match
regsub -all {[\\&]} $replacement {\\&} replacement
# Perform the replacement.
regsub -all ($match\\n)\[^\\n\]* $text \\1$replacement
}
replace "this is line 5." banana {
this is line 5.
apple
this is line 5.
another apple
this is not line 5.
yet more apples
}
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This gives the following result:
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none
this is line 5.
banana
this is line 5.
banana
this is not line 5.
yet more apples
======
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*** Second Answer ***
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[MG] offers:
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proc replace2 {args} {
if { [llength $args] < 3} {
return -code error "wrong # arguments: replace2 ?-all? ?-regexp|-glob|-exact? \$find \$replace \$text"
}
set find [lindex $args end-2]
set replace [lindex $args end-1]
set text [lindex $args end]
set args [lrange $args 0 end-3
]
set matchtype -exact
set all ""
foreach x $args {
if {$x eq "" } {
continue;
} elseif { $x eq "-all" } {
set all [list "-all"]
} elseif { $x in [list -regexp -glob -exact] } {
set matchtype $x
} else {
return -code error "unknown option '$x'"
}
}
set text [split $text \n]
set matches [lsearch {*}$all $matchtype $text $find]
if { [llength $matches] && [lindex $matches 0] != -1 } {
foreach x $matches {
incr x
set text [lreplace $text $x $x $replace]
}
}
return [join $text "\n"]
}
# Example:
replace2 -all -exact "this is line 5." banana {
this is line 5.
apple
this is line 5.
another apple
this is not line 5.
yet more apples
}
======
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*** Two Questions for One, File 13 ***
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tclamateur: Thanks for the input. In my case I'll have only two inputs. The input "match" and the input "replacement". What to give as input for "text"?
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[AMG]: Whatever text you want the substitution to be performed on. For instance, if you're working on a file, you'd supply the contents of that file.
Then write the return value back out to the file, and you're done.
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*** Boilerplate Outline on Regsub Command ***
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The regsub command in Tcl (Tool Control Language) performs substitutions based on regular expression pattern matching. Let’s dive into its usage and provide some examples:
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Basic Syntax:
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regsub ?switches? exp string subSpec ?varName?
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exp: The regular expression pattern.
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string: The input string to match against.
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subSpec: The substitution specification.
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varName (optional): If provided, the resulting string is stored in this variable, and the number of substitutions is returned.
Switches:
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-all: Causes regsub to perform the replacement in as many non-overlapping places as possible.
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Other switches (e.g., -nocase, -start index) are similar to those for regexp.
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Examples: a. Replace a specific substring in a file name:
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set filename "file.c"
regsub -- {([^\\.]+)\\.c} $filename {cc -c & -o \\1.o}
# Result: "cc -c file.c -o file.o"
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b. Convert a string template:
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set input "rand ||=> this is some text <=|| rand"
set unique1 {\\|\\|=>}
set unique2 {<=\\|\\|}
set replacement {some other text}
set new [regsub -- "($unique1).*($unique2)" $input "\\1$replacement\\2"]
puts $new
# Result: "rand ||=> some other text <=|| rand"
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c. Custom substitution using -command:
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set string "ab-cd-ef-gh"
regsub -all -command {w} $string {puts}
# Prints the letters 'a' to 'h', one per line.
======
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d. More advanced example using -command:
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set input "1234A000aadA12234"
set substring "BX"
regsub -all -command {(A[^A]*A)} $input {[string repeat $substring [expr {[string length "\\1"] / [string length $substring]}]]} new_string
puts $new_string
# Result: "1234BXBXBXBX12234"
======
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Remember that [regsub] is a powerful tool for manipulating strings using regular expressions. Feel free to experiment and adapt it to your specific needs! For more details, one can refer to the official Tcl documentation [core].
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***References on Wiki***
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'''regsub''', a [Tcl Commands%|%built-in Tcl command], performs substitutions
based on [regular expression] pattern matching.
** See Also **
[regular expressions]: information about Tcl regular expressions that is not unique to any particular command
[string map]:
[subst]:
** Synopsis **
: '''regsub''' ?''switches''? ''exp string subSpec'' ?''varName''?
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*** Extra Credit References ***
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* [Ask, and it shall be given # 11]
* [regsub]
* [Bug in regsub with "special chars"?]
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**Hidden Comments Section**
<<discussion>>
Please include your wiki MONIKER and date in your comment with the same courtesy that I will give you. Thanks, [gold] 3/26/2024
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----[gold] 3/27/2024. Note to clean up crew. Checking end of line issues here from laptop PC editor. If one sees a syntax error or brace typo error, go ahead and change. My eyes are bad on these tiny fonts.
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