In Advanced Bash-Scripting Guide, I find
Within single quotes, every special character except ' gets
interpreted literally.
So I think grep '\<the\>' file.txt would search \<the\>, instead of word the. But it searches the indeed.
#!/bin/bash
grep '\<the\>' file.txt
Added
Maybe I don't describe my question clearly.In man page,
Enclosing characters in single quotes preserves the literal value of each character within the quotes.
So my question is: Now that bash would regard enclosing characters in single quote as the literal value, why '\<the\>' is treated as the in grep? Is it grep own characteristic,differing from bash?
Indeed, bash will pass your string literally.
It is grep that interpretes the string (as a regular expression). If you want to avoid that, use grep -F. With that option, grep will search literally for the given string.
You need to add another backslash \ to match the whole pattern, as the symbols \< and \> are special to grep. Quoting the manpage: man grep
The Backslash Character and Special Expressions
The symbols \< and \> respectively match the empty string at the beginning and end
of a word.
Related
I am using sed in a shell script to edit filesystem path names. Suppose I want to replace
/foo/bar
with
/baz/qux
However, sed's s/// command uses the forward slash / as the delimiter. If I do that, I see an error message emitted, like:
▶ sed 's//foo/bar//baz/qux//' FILE
sed: 1: "s//foo/bar//baz/qux//": bad flag in substitute command: 'b'
Similarly, sometimes I want to select line ranges, such as the lines between a pattern foo/bar and baz/qux. Again, I can't do this:
▶ sed '/foo/bar/,/baz/qux/d' FILE
sed: 1: "/foo/bar/,/baz/qux/d": undefined label 'ar/,/baz/qux/d'
What can I do?
You can use an alternative regex delimiter as a search pattern by backslashing it:
sed '\,some/path,d'
And just use it as is for the s command:
sed 's,some/path,other/path,'
You probably want to protect other metacharacters, though; this is a good place to use Perl and quotemeta, or equivalents in other scripting languages.
From man sed:
/regexp/
Match lines matching the regular expression regexp.
\cregexpc
Match lines matching the regular expression regexp. The c may be any character other than backslash or newline.
s/regular expression/replacement/flags
Substitute the replacement string for the first instance of the regular expression in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the RE and the replacement. Within the RE and the replacement, the RE delimiter itself can be used as a literal character if it is preceded by a backslash.
Perhaps the closest to a standard, the POSIX/IEEE Open Group Base Specification says:
[2addr] s/BRE/replacement/flags
Substitute the replacement string for instances of the BRE in the
pattern space. Any character other than backslash or newline can
be used instead of a slash to delimit the BRE and the replacement.
Within the BRE and the replacement, the BRE delimiter itself can be
used as a literal character if it is preceded by a backslash."
When there is a slash / in theoriginal-string or the replacement-string, we need to escape it using \. The following command is work in ubuntu 16.04(sed 4.2.2).
sed 's/\/foo\/bar/\/baz\/qux/' file
I'm having a directory with many files having special characters and spaces. I want to perform an operation with all these files so I'm trying to store all filenames in a list.txt and then run the command with this list.
The special characters in my list are & []'.
So basically I want to use sed to replace each occurence with \ + the character in question.
E.g. : filename .txt => filename\ .txt etc...
The thing is I have trouble handling apostrophes.
Here is my command as of now :
ls | sed 's/\ /\\ /g' | sed 's/\&/\\&/g' | sed "s/\'/\\'/g" | sed 's/\[/\\[/g' | sed 's/\]/\\]/g'
At first I had issues with, I believe, the apostrophes in the string command in conflict with the apostrophes surrounding the string. So I used double quotes instead, but it still doesn't work.
I've tried all these and nothing worked :
sed "s/\'/\\'/g" (escaping the apostrophe)
sed "s/'/\'/g" (escaping nothing)
sed "s/'/\\'/g" (escaping the backslash)
sed 's/"'"/\"'"/g' (double quoting single quote)
As a disclaimer, I must say, I'm completely new to sed. I just run my first sed command today, so maybe I'm doing something wrong I didn't realize.
PS : I've seen those thread, but no answer worked for me :
https://unix.stackexchange.com/questions/157076/how-to-remove-the-apostrophe-and-delete-the-space
How to replace to apostrophe ' inside a file using SED
This may do:
cat file
avbadf
test&rr
more [ yes
this ]
and'df
sed -r 's/(\x27|&|\[|\])/\\\1/g' file
avbadf
test\&rr
more \[ yes
this \]
and\'df
\x27 is equal to singe quote '
\x22 is equal to double quote "
Whoops, I found the answer to my question. Here is the working input :
sed "s/'/\\\'/g"
This will effectively replace any ' with \'.
However I'm having trouble understanding exactly what's happening here.
So if I understand correctly, we are escaping the backslash and the apostrophe in the replacement string. Now, if somebody could answer some those, I would be grateful :
Why don't we need to escape the first quote (the one in the pattern to find) ?
Why do we have to escape the backslash whereas for the other characters, there's no need ?
Why do we need to escape the second quote (the one in the replacement string) ?
I think all of your sed matches actually need that replacement pattern. This one seems to work for all examples:
ls | sed "s/\ /\\\ /g" | sed "s/\&/\\\&/g" | sed "s/\[/\\\[/g" | sed "s/\]/\\\]/g" | sed "s/'/\\\'/g"
So it is s/regex/replacement/command and 'regex' and 'replacement' have different sets of special characters.
The only one that's different is s/'/\\\'/g and there only because I don't believe there is any special ' character on the regex expression. There is some obscure \' special character in the replacement expression, for matching buffer ends in multi-line mode, accord to the docs. That might be why it needs an escape in the replacement side, but not in the regex side.
For example, \5 is a special character in the replacement expression, so to replace:
filename5.txt -> filename\5.txt
You would also need, as with apostrophe:
sed "s/5/\\\5/g"
It probably has to do with the mysterious inner works of sed parsing, it might read from right to left or something.
Please try the following:
sed 's/[][ &'\'']/\\&/g' file
By using the same example by #Jotne, the result will be:
gavbadf
gtest\&rr
gmore\ \[\ yes
gthis\ \]
gand\'df
[How it works]
The regex part in the sed s command above just defines a character
class of & []', which should be escaped with a backslash.
The right square bracket ] does not need escaping when put
immediately after the left square bracket [.
The obfuscating part will be the handling of a single quote.
We cannot put a single quote within single quotes even if we escape it.
The workaround is as follows: Say we have an assignment str='aaabbb'.
To put a single quote between "aaa" and "bbb", we can say as
str='aaa'\''bbb'.
It may look puzzling but it just concatenates the three sequences;
1) to close the single-quoted string as 'aaa'.
2) to put a single quote with an escaping backslash as \'.
3) to restart the single-quoted string as 'bbb'.
Hope this helps.
I am trying to grep the string
"SNTCHDCS06-Filesystem D:\\ Label:Data Serial Number f8271450"
from a csv file, but somehow I failed miserably.
I understand that I need to add two backlashes on top of the two backslashes (one for shell, one for bash), but it doesn't work after that.
The below command works.
[root#nagiospdc01 folder]# grep -e "^SNTCHDCS06-Filesystem D:\\\\" in/masterlist.csv
SNTCHDCS06-Filesystem D:\\ Label:Data Serial Number f8271450,SNTCHDCS06,10.24.64.210,Active Directory,AD Server,UCS,Filesystem D:\\ Label:Data Serial Number f8271450,Windows Team,0,XM_OPS_WIN,Windows Team,Y,Y,N,N,Y,Y,Y,Y,Y,N,N,Y,Y,ITOC
When I try to grep for the space after that, grep doesn't work and simply fails.
[root#nagiospdc01 folder]# grep -e "^SNTCHDCS06-Filesystem D:\\\\ " in/masterlist.csv
Appreciate if someone can enlighten me on the correct grep syntax and command.
Use single quotes,
grep -e '^SNTCHDCS06-Filesystem D:\\ Label:Data Serial Number f8271450'
When using double quotes \\ gets converted to a single \ by bash. However bash does not look inside single quotes.
From the Bash manual:
3.1.2.2 Single Quotes
Enclosing characters in single quotes (') preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.
3.1.2.3 Double Quotes
Enclosing characters in double quotes (") preserves the literal value of all characters within the quotes, with the exception of $, `, \, and, when history expansion is enabled, !. The characters $ and ` retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: $, `, ", \, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ! appearing in double quotes is escaped using a backslash. The backslash preceding the ! is not removed.
The special parameters * and # have special meaning when in double quotes (see Shell Parameter Expansion).
The -F option in grep allows to search for fixed strings. Also the single quotes helps to search for the exact string.
-F, --fixed-strings :
Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched.
grep -F 'SNTCHDCS06-Filesystem D:\\ Label:Data Serial Number f8271450' masterlist.csv
*SNTCHDCS06-Filesystem D:\\ Label:Data Serial Number f8271450*
Below is the string I am trying to grep for this in the bash shell:
'#Hostname=sometext.company.com, sometext.company.com' filename
I want to only find the string if it matches that exact pattern. I already tried the command below and a few others.
grep -Fx "#Hostname=sometext.company.com, sometext.company.com" filename
Did you specify the -xoption on purpose?
grep -F '#Hostname=sometext.company.com, sometext.company.com' filename
most likely is what you want. Also, it's better to put single quotes instead of double quotes, just in case your search pattern happens to contain special shell characters.
I was trying to search for a particular word BML.I in a current directory.
When I tried with the below command:
grep -l "BML.I" *
It is displaying all the results if it contains the word BML
Is it possible to grep for the exact match BML.I
You need to escape the . (period) since by default it matches against any character, and specify -w to match a specific word e.g.
grep -w -l "BML\.I" *
Note there are two levels of escaping in the above. The quotes ensure that the shell passes BML\.I to grep. The \ then escapes the period for grep. If you omit the quotes, then the shell interprets the \ as an escape for the period (and would simply pass the unescaped period to grep)
try grep -wF
from man page:
-w, --word-regexp
Select only those lines containing matches that form whole words. The
test is that the matching substring must either be at the beginning of
the line, or preceded by a non-word constituent character. Similarly, it
must be either at the end of the line or followed by a non-word
constituent character. Word-constituent characters are letters, digits,
and the underscore.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by newlines, any
of which is to be matched. (-F is specified by POSIX.)
I use fgrep, which is the same as grep -F
Use this command:
ls | grep -x "BML.I"