regexp and "\" (backslash)?
Joachim Martin
(tclsh 7.3)
% set s "this is a \\"
this is a \
% regexp "\" $s
"
wrong # args: should be "regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?"
% regexp \ $s
wrong # args: should be "regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?"
% regexp "\\" $s
couldn't compile regular expression pattern: trailing \
% regexp \\ $s
couldn't compile regular expression pattern: trailing \
Please, someone show me the way and make me feel sheepish... -Joachim
-------------------------
Joachim Martin jma...@elmer.harvard.edu
Systems Librarian http://sirin.harvard.edu/~jmartin
Office for Information Systems Harvard University Library
Hume C.L. Smith
JM> How do I regexp for a backslash? The following doesn't work for me:
JM> (tclsh 7.3)
JM> % set s "this is a \\"
JM> this is a \
JM> % regexp "\" $s
JM> "
JM> wrong # args: should be "regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?"
JM> % regexp \ $s
JM> wrong # args: should be "regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?"
JM> % regexp "\\" $s
JM> couldn't compile regular expression pattern: trailing \
JM> % regexp \\ $s
JM> couldn't compile regular expression pattern: trailing \
JM> Please, someone show me the way and make me feel sheepish... -Joachim
regexp \\\\ $s
regexp {\\} $s
you need to get two backslashes (backsolidii?) into regexp - one to
escape the other in regexp meaning.
without braces, the \s have meaning to the reader, so you have to
escape each \ again - so you need four.
with braces, \s are pretty much ignored - so you can just write the
two backslashes regexp needs.
(\s count inside braces - set a {\} is considered incomplete - but
they survive in the string represented - set a {\}} sets a to \} ).
regexp is one of the nicest features of tcl - how i wish sh had it -
but it's also often painful to use, because RE syntax collides with
tcl's (e.g. brackets). sometimes you can put the RE in braces, but
often you want to use things like \t, etc. etc... the quoting hell
that's usually avoided by tcl as compared to sh, happens to reappear
in this case. perhaps there's a computer-linguistic law, of
conservation of quoting hell? :-)
--
Hume Smith hcls...@ra.isisnet.com
"Ah. Left brain! Foop." thumb
u01mtm
: How do I regexp for a backslash? The following doesn't work for me:
: (tclsh 7.3)
: % set s "this is a \\"
: this is a \
[attempts deleted]
: Please, someone show me the way and make me feel sheepish... -Joachim
: -------------------------
: Joachim Martin jma...@elmer.harvard.edu
: Systems Librarian http://sirin.harvard.edu/~jmartin
: Office for Information Systems Harvard University Library
Try :
% set s "this is a \\"
this is a \
regexp "\\\\" $s
1
The reason the above works is because when the command line is evaluated the
"\\\\" is expanded (reduced) to "\\" (i.e. is treats it as two "\\"'s)
the "\\" is then passed to the regexp routine which then evaluates it to "\"
Hope this helps.
Mike.
Donal K. Fellows
>Joachim Martin (jmartin@elmer) wrote:
>: How do I regexp for a backslash? The following doesn't work for me:
>: (tclsh 7.3)
>: % set s "this is a \\"
>: this is a \
>
>
>Try :
>
>regexp "\\\\" $s
>1
>
>The reason the above works is because when the command line is evaluated the
>"\\\\" is expanded (reduced) to "\\" (i.e. is treats it as two "\\"'s)
>the "\\" is then passed to the regexp routine which then evaluates it to "\"
>
You could also try using {} to quite your regexp, as in:
regexp {\\} $s
1
as this gets rid of _one_ of the layers of backslashitis...
Donal.
--
Donal K. Fellows, (at work) | Donal K. Fellows, (at home)
Dept. of Computer Science, | 6, Randall Place, Heaton,
University of Manchester | Bradford, BD9 4AE
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