When using the following code to check about the content of a text file (test.txt),
I get a blank screen and to quit by cntrl+C.

@echo off
findstr ^/ test.txt > nul
if %errorlevel%==0 (
echo Found!
) else (
echo No matches found
)
pause
exit

It works fine for ^\, ^| and ^?

Any idea about the problem?

Thanks,
Thomas Try:

Findstr /C:/ Test.txt > Nul

The others (\ ?) will probably work without being escaped, the pipe char will always have to be escaped.

Good luck.

Yes, it works perfect.

May I know the reaon to add c:/ ?

Thanks,
Thomas

In Findstr /C: is a switch and the following / is the string to be found as a literal. Don't CONFUSE the switch /C: with the partition C:\

Entered at the Command Prompt Findstr/? shows:
Quote

Searches for strings in files.

FINDSTR [/B] [/E] [/L] [/R] [/S] [/I] [/X] [/V] [/N] [/M] [/O] [/P] [/F:file]
[/C:string] [/G:file] [/D:dir list] [/A:color attributes] [/OFF[liNE]]
strings [[drive:][path]FILENAME[ ...]]

/B Matches pattern if at the beginning of a line.
/E Matches pattern if at the end of a line.
/L Uses search strings literally.
/R Uses search strings as regular expressions.
/S Searches for matching files in the current directory and all
subdirectories.
/I Specifies that the search is not to be case-sensitive.
/X Prints lines that match exactly.
/V Prints only lines that do not contain a match.
/N Prints the line number before each line that matches.
/M Prints only the filename if a file contains a match.
/O Prints CHARACTER offset before each matching line.
/P Skip files with non-printable characters.
/OFF[liNE] Do not skip files with offline attribute set.
/A:attr Specifies color attribute with TWO hex digits. See "color /?"
/F:file Reads file list from the specified file(/ stands for console).
/C:string Uses specified string as a literal search string.
/G:file Gets search strings from the specified file(/ stands for console).
/D:dir Search a semicolon delimited list of directories
strings Text to be searched for.
[drive:][path]filename
Specifies a file or files to search.

Use spaces to separate multiple search strings unless the argument is prefixed
with /C. For EXAMPLE, 'FINDSTR "hello there" x.y' searches for "hello" or
"there" in file x.y. 'FINDSTR /C:"hello there" x.y' searches for
"hello there" in file x.y.

Regular expression quick reference:
. Wildcard: any character
* Repeat: zero or more occurances of previous character or class
^ Line position: beginning of line
$ Line position: end of line
[class] Character class: any one character in set
[^class] Inverse class: any one character not in set
[x-y] Range: any characters within the specified range
\x Escape: literal use of metacharacter x
\<xyz Word position: beginning of word
xyz\> Word position: end of word

For full information on FINDSTR regular expressions refer to the online Command
Reference.