In that case, the value of x inside AWK is vulnerable to regular expression metacharacters. Say, for example, that you wanted to match a pathname that had a dot. The dot would not be treated literally, but would be a wildcard matching any character. In the following example, it yields a false positive.
There's simply no way around it. Unless you are absolutely certain that there will be no metacharacters involved, you cannot pass a value through SED or AWK's regular expression parsers (or AWK's string parser) without passing that value through some sort of sanitizing step to properly escape those special characters (which would be something of a nightmare if it had to be made safe to pass through AWK's string parsing before arriving at the regular expressioin parsing stage).
Alister
---------- Post updated at 01:18 PM ---------- Previous update was at 01:15 PM ----------
cue:
Now that i think about it, by far the simplest solution to this is fgrep. I became fixated on AWK and sed since they were listed in the original post. Unless I missed something, the following should work just fine and is not susceptible to metacharacter interference.
Hello
I am new to shell scripting and can anyone tell me how to check if there are any special characters in a file. Can i use grep ?
thanks
susie (2 Replies)
Hello,
I have a requirement to search a directory, which contains any number of other directories for file names that contain special characters.
directory structure
DIR__
|__>DIR1
|__>DIR2__
|__>DIR2.1
|__>DIR2.2
|__>DIR3
..
... (8 Replies)
i'm puzzled....
trying to look for the pattern }"'. but the below code returns to me the message below (pattern is curley queue + dbl qt + sng qt + period)
nawk -v pat="\}\"\'\."'
{
if (match($0, pat)) {
before = substr($0,1,RSTART-1);
... (11 Replies)
Hi,
On AIX 5200-07-00 I have a find command as following to delete files from a certain location that are more than 7 days old. I am being told that I cannot use -exec option to delete files from these directories.
Having said that I am more curious to know how this can be done.
an sample... (3 Replies)
Hi all,
I have the following lines
<b>A gtwrhwrthwr text hghthwrhtwrtw </b><font color='#06C'>; text text (text)
<b>B gtwrhwrthwr text hghthwrhtwrtw </b><font color='#06C'>; text text (text)
<b>J gtwrhwrthwr text hghthwrhtwrtw </b><font color='#06C'>; text text (text)
and I would like to... (5 Replies)
I'm looking for SED equivalent for grep -w -f. All I want is to search a list of patterns from a file. Also If the pattern doesn't match I do not want "null returned", rather I would prefer some text as place holder say "BLANK LINE" as I intend to process the output file based on line number.
... (1 Reply)
Hello All,
I am here again scratching my head on pattern selection with special characters.
I have a large file having around 200 entries and i have to select a single line based on a pattern.
I am able to do that:
Code:
cat mytest.txt | awk -F: '/myregex/ { print $2}'
... (6 Replies)
Hi all,
I have a list which I want to search in another file.
I can do that using
grep -f
but the search is failing due to special characters, how do I solve this?
One row in that list is
amino-acid permease inda1 gb|EDU41782.1| amino-acid permease inda1 Input file to be searched... (2 Replies)
Hello Team,
Any help would be much appreciated for the below scenario:
I have a sed command below where I am trying to replace the contents of 'old_pkey' variable with 'new_pkey' variable in a Soap request file (delete_request.txt). This works fine for regular string values, but this new_pkey... (8 Replies)
Discussion started by: ChicagoBlues
8 Replies
LEARN ABOUT PHP
regex
regex(1F) FMLI Commands regex(1F)NAME
regex - match patterns against a string
SYNOPSIS
regex [-e] [ -v "string"] [ pattern template] ... pattern [template]
DESCRIPTION
The regex command takes a string from the standard input, and a list of pattern / template pairs, and runs regex() to compare the string
against each pattern until there is a match. When a match occurs, regex writes the corresponding template to the standard output and
returns TRUE. The last (or only) pattern does not need a template. If that is the pattern that matches the string, the function simply
returns TRUE. If no match is found, regex returns FALSE.
The argument pattern is a regular expression of the form described in regex(). In most cases, pattern should be enclosed in single quotes
to turn off special meanings of characters. Note that only the final pattern in the list may lack a template.
The argument template may contain the strings $m0 through $m9, which will be expanded to the part of pattern enclosed in ( ... )$0 through
( ... )$9 constructs (see examples below). Note that if you use this feature, you must be sure to enclose template in single quotes so
that FMLI does not expand $m0 through $m9 at parse time. This feature gives regex much of the power of cut(1), paste(1), and grep(1), and
some of the capabilities of sed(1). If there is no template, the default is $m0$m1$m2$m3$m4$m5$m6$m7$m8$m9.
OPTIONS
The following options are supported:
-e Evaluates the corresponding template and writes the result to the standard output.
-v "string" Uses string instead of the standard input to match against patterns.
EXAMPLES
Example 1: Cutting letters out of a string
To cut the 4th through 8th letters out of a string (this example will output strin and return TRUE):
`regex -v "my string is nice" '^.{3}(.{5})$0' '$m0'`
Example 2: Validating input in a form
In a form, to validate input to field 5 as an integer:
valid=`regex -v "$F5" '^[0-9]+$'`
Example 3: Translating an environment variable in a form
In a form, to translate an environment variable which contains one of the numbers 1, 2, 3, 4, 5 to the letters a, b, c, d, e:
value=`regex -v "$VAR1" 1 a 2 b 3 c 4 d 5 e '.*' 'Error'`
Note the use of the pattern '.*' to mean "anything else".
Example 4: Using backquoted expressions
In the example below, all three lines constitute a single backquoted expression. This expression, by itself, could be put in a menu defini-
tion file. Since backquoted expressions are expanded as they are parsed, and output from a backquoted expression (the cat command, in this
example) becomes part of the definition file being parsed, this expression would read /etc/passwd and make a dynamic menu of all the login
ids on the system.
`cat /etc/passwd | regex '^([^:]*)$0.*$' '
name=$m0
action=`message "$m0 is a user"`'`
DIAGNOSTICS
If none of the patterns match, regex returns FALSE, otherwise TRUE.
NOTES
Patterns and templates must often be enclosed in single quotes to turn off the special meanings of characters. Especially if you use the
$m0 through $m9 variables in the template, since FMLI will expand the variables (usually to "") before regex even sees them.
Single characters in character classes (inside []) must be listed before character ranges, otherwise they will not be recognized. For exam-
ple, [a-zA-Z_/] will not find underscores (_) or slashes (/), but [_/a-zA-Z] will.
The regular expressions accepted by regcmp differ slightly from other utilities (that is, sed, grep, awk, ed, and so forth).
regex with the -e option forces subsequent commands to be ignored. In other words, if a backquoted statement appears as follows:
`regex -e ...; command1; command2`
command1 and command2 would never be executed. However, dividing the expression into two:
`regex -e ...``command1; command2`
would yield the desired result.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO awk(1), cut(1), grep(1), paste(1), sed(1), regcmp(3C), attributes(5)SunOS 5.10 12 Jul 1999 regex(1F)