---
name: "visual-regexp"
section: "1"
platform: "linux"
package: "visual-regexp"
version: "3.1-7"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/visual-regexp"
---
# visual-regexp(1)
graphical front-end to write/debug regular expression
## NAME
**visual-regexp** - graphical front-end to write/debug regular expression
## SYNOPSIS
```
visual-regexp file
```
## DESCRIPTION
**visual-regexp is a program that interactively creates and shows the output** **from regular expressions in Perl. It is ideal for debugging complicated perl** **expressions.**
**Helps you to design, debug or more generally work with perl regular expression.** **As it is often difficult to write the right regexp at the first try, this** **tool will show you the effect of your regexp on a sample you can choose.**
## DESIGN OF REGEXP
**To design regexp, just type the expression in the top text widget.** **Press the 'Go' button to highlight the matched part of the text in the sample** **text widget.**
**To get a quickref of the regexp syntax use the menu 'View/Show regexp help'.**
**You can specify some options using the checkboxes (please read Tcl help to** **learn the meaning of these options).**
## RECURSIVE DESIGN OF REGEXPS
**Sometimes you will need more than one step to extract the information you want** **from the sample. For example, imagine you want to retrieve information from** **an HTML table inside an another HTML table :**
```
```
**You cannot use one global regexp to extract the two lines "One 1" and "Two 2".** **You have to use a first regexp to narrow the processed region.** **Type the following regexp '\\]\*?\>(.\*?)\' and press 'Go'.** **You see now that the interesting area is shown in blue. Press the Match '1'** **button which will extract the blue text (the regexp to use to get this text** **is then printed on the console).** **Now use '\(.\*?)\.\*?\(.\*?)\' to get the information you need.**
## OPTIMIZATION OF REGEXPS
**When you need to match a list of words, use the menu** **’Insert regexp/Make regexp' to design an optimized version of the word list.**
**For example, the list 'aa aab ab ad' is optimized into 'a(ab?\|b\|d)'.**
## PROCESSING THE SAMPLE TEXT
**Can use visual-regexp to perform modification of a text.** **Just use the menu 'Select mode/Use replace'. You can now design a regexp to** **match what you want. Then use the replace text widget to enter the substitution** **you want to apply (use , 1, 2, ... to match the subregexp, use the color** **to map the number with the matched sub-expressions).**
**After the substitution, you can save the new text using the 'File/Save ...'** **menu. You can let the program choose the end-of-line format or force them for** **a specific environment (Unix, Windows, Mac).**
## KNOWN PROBLEMS
- •
**Some regexp can consume a lot of CPU time. This seems to be caused by the use** **of -all, -inline and -indices flags together.**
- •
**When a subexpression is not matched (empty match), the last character of the** **previous match are coloured. This is due to a problem in Tcl (bug submitted to** **Scriptics).**
## REGULAR EXPRESSIONS IN PERL
**METACHARACTERS**
- **"^"**
**beginning of string**
- **"$"**
**end of string**
- **"."**
**any character except newline**
- **"\*"**
**match 0 or more times**
- **"+"**
**match 1 or more times**
- **"?"**
**match 0 or 1 times; or: shortest match**
- **"\|"**
**alternative**
- **"( )"**
**grouping; “storing”**
- **"\[ \]"**
**set of characters**
- **"{ }"**
**repetition modifier**
- **"\\"**
**quote or special**
**REPETITION**
- **a\***
**zero or more a’s**
- **a+**
**one or more a’s**
- **a?**
**zero or one a’s (i.e., optional a)**
- **a{m}**
**exactly m a’s**
- **a{m,}**
**at least m a’s**
- **a{m,n}**
**at least m but at most n a’s**
- **repetition?**
**same as repetition but the shortest match is taken**
**SPECIAL NOTATIONS WITH \\**
```
Single characters
\t tab
\n newline
\r return (CR)
\xhh character with hex. code hh
“Zero-width assertions”
\b “word” boundary
\B not a “word” boundary
Matching
\w matches any single character classified as a “word” character (alphanumeric or “_”)
\W matches any non-“word” character
\s matches any whitespace character (space, tab, newline)
\S matches any non-whitespace character
\d matches any digit character, equivalent to [0-9]
\D matches any non-digit character
```
**CHARACTER SETS: SPECIALITIES INSIDE \[...\]**
- **\[characters\]**
**matches any of the characters in the sequence**
- **\[x-y\]**
**matches any of the characters from x to y (inclusively) in the ASCII code**
- **\[\\-\]**
**matches the hyphen character “-”**
- **\[\\n\]**
**matches the newline; other single character denotations with apply normally, too**
- **\[^something\]**
**matches any character except those that \[something\] denotes; that is, immediately after the leading “\[”, the circumflex “^” means “not” applied to all of the rest**
## EXAMPLES
- **abc**
**abc (that exact character sequence, but anywhere in the string)**
- **^abc**
**abc at the beginning of the string**
- **abc$**
**abc at the end of the string**
- **a\|b**
**either of a and b**
- **^abc\|abc$**
**the string abc at the beginning or at the end of the string**
- **ab{2,4}c**
**an a followed by two, three or four b’s followed by a c**
- **ab{2,}c**
**an a followed by at least two b’s followed by a c**
- **ab\*c**
**an a followed by any number (zero or more) of b’s followed by a c**
- **ab+c**
**an a followed by one or more b’s followed by a c**
- **ab?c**
**an a followed by an optional b followed by a c; that is, either abc or ac**
- **a.c**
**an a followed by any single character (not newline) followed by a c**
- **a\\.c**
**a.c exactly**
- **\[abc\]**
**any one of a, b and c**
- **\[Aa\]bc**
**either of Abc and abc**
- **\[abc\]+**
**any (nonempty) string of a’s, b’s and c’s (such as a, abba, acbabcacaa)**
- **\[^abc\]+**
**any (nonempty) string which does not contain any of a, b and c (such as 'defg')**
- **\\d\\d**
**any two decimal digits, such as 42; same as \\d{2}**
- **\\w+**
**a “word”: a nonempty sequence of alphanumeric characters and low lines (underscores), such as foo and 12bar8 and foo\_1**
- **100\\s\*mk**
**the strings 100 and mk optionally separated by any amount of white space (spaces, tabs, newlines)**
- **abc\\b**
**abc when followed by a word boundary (e.g. in abc! but not in abcd)**
- **perl\\B**
**perl when not followed by a word boundary (e.g. in perlert but not in perl stuff)**
## REQUIREMENTS
**This program requires Tcl/Tk 8.3.0 or later with the script version.** **Nothing with the standalone program.**
## SEE ALSO
**[perlre(1)](/perlre/1.md), [perlrequick(1)](/perlrequick/1.md)**
## AUTHOR
**visual-regexp was written by Laurent Riesterer \.**
**This manual page was written by Braulio Henrique Marques Souto \** **for the Debian project (but may be used by others).**