i have a file which contains several instances of \n.
i would like to replace them with actual newlines, but sed doesn't recognize the \n.
i tried
sed -r -e 's/\n/\n/'
sed -r -e 's/\\n/\n/'
sed -r -e 's/[\n]/\n/'
and many other ways of escaping it.
is sed able to recognize a literal \n? if so, how?
is there another program that can read the file interpreting the \n's as real newlines?
Can you please try this
sed -i 's/\\n/\n/g' input_filename
What exactly works depends on your sed implementation. This is poorly specified in POSIX so you see all kinds of behaviors.
The -r option is also not part of the POSIX standard; but your script doesn't use any of the -r features, so let's just take it out. (For what it's worth, it changes the regex dialect supported in the match expression from POSIX "basic" to "extended" regular expressions; some sed variants have an -E option which does the same thing. In brief, things like capturing parentheses and repeating braces are "extended" features.)
On BSD platforms (including MacOS), you will generally want to backslash the literal newline, like this:
sed 's/\\n/\
/g' file
On some other systems, like Linux (also depending on the precise sed version installed -- some distros use GNU sed, others favor something more traditional, still others let you choose) you might be able to use a literal \n in the replacement string to represent an actual newline character; but again, this is nonstandard and thus not portable.
If you need a properly portable solution, probably go with Awk or (gasp) Perl.
perl -pe 's/\\n/\n/g' file
In case you don't have access to the manuals, the /g flag says to replace every occurrence on a line; the default behavior of the s/// command is to only replace the first match on every line.
awk seems to handle this fine:
echo "test \n more data" | awk '{sub(/\\n/,"**")}1'
test ** more data
Here you need to escape the \ using \\
$ echo "\n" | sed -e 's/[\\][n]/hello/'
sed works one line at a time, so no \n on 1 line only (it's removed by sed at read time into buffer). You should use N, n or H,h to fill the buffer with more than one line, and then \n appears inside. Be careful, ^ and $ are no more end of line but end of string/buffer because of the \n inside.
\n is recognized in the search pattern, not in the replace pattern. Two ways for using it (sample):
sed s/\(\n\)bla/\1blabla\1/
sed s/\nbla/\
blabla\
/
The first uses a \n already inside as back reference (shorter code in replace pattern);
the second use a real newline.
So basically
sed "N
$ s/\(\n\)/\1/g
"
works (but is a bit useless). I imagine that s/\(\n\)\n/\1/g is more like what you want.
Related
This question already has answers here:
Replace whole line when match found with sed
(4 answers)
Closed 4 years ago.
How do I find line starts with and replace complete line?
File output:
xyz
abc
/dev/linux-test1/
Code:
output=/dev/sda/windows
sed 's/^/dev/linux*/$output/g' file.txt
I am getting below Error:
sed: -e expression #1, char 9: unknown option to `s'
File Output expected after replacement:
xyz
abc
/dev/sda/windows
Let's take this in small steps.
First we try changing "dev" to "other":
sed 's/dev/other/' file.txt
/other/linux-test1/
(Omitting the other lines.) So far, so good. Now "/dev/" => "/other/":
sed 's//dev///other//' file.txt
sed: 1: "s//dev///other//": bad flag in substitute command: '/'
Ah, it's confused, we're using '/' as both a command delimiter and literal text. So we use a different delimiter, like '|':
sed 's|/dev/|/other/|' file.txt
/other/linux-test1/
Good. Now we try to replace the whole line:
sed 's|^/dev/linux*|/other/|' file.txt
/other/-test1/
It didn't replace the whole line... Ah, in sed, '*' means the previous character repeated any number of times. So we precede it with '.', which means any character:
sed 's|^/dev/linux.*|/other/|' file.txt
/other/
Now to introduce the variable:
sed 's|^/dev/linux.*|$output|' file.txt
$output
The shell didn't expand the variable, because of the single quotes. We change to double quotes:
sed "s|^/dev/linux.*|$output|" file.txt
/dev/sda/windows
This might work for you (GNU sed):
output="/dev/sda/windows"; sed -i '\#/dev/linux.*/#c'"$output" file
Set the shell variable and change the line addressed by /dev/linux.*/ to it.
N.B. The shell variable needs to interpolated hence the ; i.e. the variable may be set on a line on its own. Also the the delimiter for the sed address must be changed so as not to interfere with the address, hence \#...#, and finally the shell variable should be enclosed in double quotes to allow full interpolation.
I'd recommend not doing it this way. Here's why.
Sed is not a programming language. It's a stream editor with some constructs that look and behave like a language, but it offers very little in the way of arbitrary string manipulation, format control, etc.
Sed only takes data from a file or stdin (also a file). Embedding strings within your sed script is asking for errors -- constructs like s/re/$output/ are destined to fail at some point, almost regardless of what workarounds you build into your sed script. The best solutions for making sed commands like this work is to do your input sanitization OUTSIDE of sed.
Which brings me to ... this may be the wrong tool for this job, or might be only one component of the toolset for the job.
The error you're getting is obviously because the sed command you're using is horribly busted. The substitute command is:
s/pattern/replacement/flags
but the command you're running is:
s/^/dev/linux*/$output/g
The pattern you're searching for is ^, the null at the beginning of the line. Your replacement pattern is dev, then you have a bunch of text that might be interpreted as flags. This plainly doesn't work, when your search string contains the same character that you're using as a delimiter to the options for the substitute command.
In regular expressions and in sed, you can escape things. You while you might get some traction with s/^\/dev\/linux.*/$output/, you'd still run into difficulty if $output contained slashes. If you're feeding this script to sed from bash, you could use ${output//\//\\\/}, but you can't handle those escapes within sed itself. Sed has no variables.
In a proper programming language, you'd have better separation of variable content and the commands used for the substitution.
output="/dev/sda/windows"
awk -v output="$output" '$1~/\/dev\/linux/ { $0=output } 1' file.txt
Note that I've used $1 here because in your question, your input lines (and output) appear to have a space at the beginning of each line. Awk automatically trims leading and trailing space when assigning field (positional) variables.
Or you could even do this in pure bash, using no external tools:
output="/dev/sda/windows"
while read -r line; do
[[ "$line" =~ ^/dev/linux ]] && line="$output"
printf '%s\n' "$line"
done < file.txt
This one isn't resilient in the face of leading whitespace. Salt to taste.
So .. yes, you can do this with sed. But the way commands get put together in sed makes something like this risky, and despite the available workarounds like switching your substitution command delimiter to another character, you'd almost certainly be better off using other tools.
I am trying to convert 2015-06-03_18-05-30 to 20150603180530 using sed.
I have this:
$ var='2015-06-03_18-05-30'
$ echo $var | sed 's/\-\|\_//g'
$ echo $var | sed 's/-|_//g'
None of these are working. Why is the alternation not working?
As long as your script has a #!/bin/bash (or ksh, or zsh) shebang, don't use sed or tr: Your shell can do this built-in without the (comparatively large) overhead of launching any external tool:
var='2015-06-03_18-05-30'
echo "${var//[-_]/}"
That said, if you really want to use sed, the GNU extension -r enables ERE syntax:
$ sed -r -e 's/-|_//g' <<<'2015-06-03_18-05-30'
20150603180530
See http://www.regular-expressions.info/posix.html for a discussion of differences between BRE (default for sed) and ERE. That page notes, in discussing ERE extensions:
Alternation is supported through the usual vertical bar |.
If you want to work on POSIX platforms -- with /bin/sh rather than bash, and no GNU extensions -- then reformulate your regex to use a character class (and, to avoid platform-dependent compatibility issues with echo[1], use printf instead):
printf '%s\n' "$var" | sed 's/[-_]//g'
[1] - See the "APPLICATION USAGE" section of that link, in particular.
Something like this ought to do.
sed 's/[-_]//g'
This reads as:
s: Search
/[-_]/: for any single character matching - or _
//: replace it with nothing
g: and do that for every character in the line
Sed operates on every line by default, so this covers every instance in the file/string.
I know you asked for a solution using sed, but I offer an alternative in tr:
$ var='2015-06-03_18-05-30'
$ echo $var | tr -d '_-'
20150603180530
tr should be a little faster.
Explained:
tr stands for translate and it can be used to replace certain characters with another ones.
-d option stands for delete and it removes the specified characters instead of replacing them.
'_-' specifies the set of characters to be removed (can also be specified as '\-_' but you need to escape the - there because it's considered another option otherwise).
Easy:
sed 's/[-_]//g'
The character class [-_] matches of the characters from the set.
sed 's/[^[:digit:]]//g' YourFile
Could you tell me what failed on echo $var | sed 's/\-\|\_//g', it works here (even if escapping - and _ are not needed and assuming you use a GNU sed due to \| that only work in this enhanced version of sed)
I need to replace within a little bash script a string inside a file but... I am getting weird results.
Let's say I want to replace:
<tag><![CDATA[text]]></tag>
With:
<tag><![CDATA[replaced_text]]></tag>
Should I use sed? I think due to / and [ ] I am getting weird results...
What would be the best way of approaching this?
Perl with -p option works almost as sed and it has \Q (quote) switch for its regexes:
perl -pe 's{\Q<tag><![CDATA[text]]></tag>}
{<tag><![CDATA[replaced_text]]></tag>}' YOUR_FILE
And in Perl you can use different punctuation to delimiter your expressions (s{...}{...} in my example).
Yes, you need to escape the brackets, and either escape slashes or use different delimiters.
sed 's,<tag><!\[CDATA\[text\]\]></tag>,<tag><!\[CDATA\[replaced)text\]\]></tag>,'
That said, SGML and XML are not actually any better than HTML when it comes to using regexes; don't expect this to generalize.
This should be enough:
$ echo '<tag><![CDATA[text]]></tag>' | sed 's/\[text\]/\[replaced_text\]/'
<tag><![CDATA[replaced_text]]></tag>
You can also change your / separator inside sed to a different character like ,, | or %.
Just use a delimiter other than /, here I use #:
sed -i 's#<tag><!\[CDATA\[text\]\]></tag>#<tag><![CDATA[replaced_text]]></tag>#g' filename
-i to have sed change the file instead of printing it out.
g is for matching more than once (global).
But do you know the exact string you want to match, both the tag and the text?
For instance, if you want to replace the text in all with your replaced_text:
perl -i -pe 's#(<tag><!\[CDATA\[)(.*?)(\]\]></tag>)#\1replaced_text\3#g' filename
Switched to perl because sed doesn't support non-greedy multipliers (the *?).
How can I fix this:
abc="a/b/c"; echo porc | sed -r "s/^/$abc/"
sed: -e expression #1, char 7: unknown option to `s'
The substitution of variable $abc is done correctly, but the problem is that $abc contains slashes, which confuse sed. Can I somehow escape these slashes?
Note that sed(1) allows you to use different characters for your s/// delimiters:
$ abc="a/b/c"
$ echo porc | sed -r "s|^|$abc|"
a/b/cporc
$
Of course, if you go this route, you need to make sure that the delimiters you choose aren't used elsewhere in your input.
The GNU manual for sed states that "The / characters may be uniformly replaced by any other single character within any given s command."
Therefore, just use another character instead of /, for example ::
abc="a/b/c"; echo porc | sed -r "s:^:$abc:"
Do not use a character that can be found in your input. We can use : above, since we know that the input (a/b/c/) doesn't contain :.
Be careful of character-escaping.
If using "", Bash will interpret some characters specially, e.g. ` (used for inline execution), ! (used for accessing Bash history), $ (used for accessing variables).
If using '', Bash will take all characters literally, even $.
The two approaches can be combined, depending on whether you need escaping or not, e.g.:
abc="a/b/c"; echo porc | sed 's!^!'"$abc"'!'
You don't have to use / as pattern and replace separator, as others already told you. I'd go with : as it is rather rarely used in paths (it's a separator in PATH environment variable). Stick to one and use shell built-in string replace features to make it bullet-proof, e.g. ${abc//:/\\:} (which means replace all : occurrences with \: in ${abc}) in case of : being the separator.
$ abc="a/b/c"; echo porc | sed -r "s:^:${abc//:/\\:}:"
a/b/cporc
backslash:
abc='a\/b\/c'
space filling....
As for the escaping part of the question I had the same issue and resolved with a double sed that can possibly be optimized.
escaped_abc=$(echo $abc | sed "s/\//\\\AAA\//g" | sed "s/AAA//g")
The triple A is used because otherwise the forward slash following its escaping backslash is never placed in the output, no matter how many backslashes you put in front of it.
I want to do some simple string replace in Bash with sed. I am Ubuntu 10.10.
Just see the following code, it is self-explanatory:
name="A%20Google.."
echo $name|sed 's/\%20/_/'|sed 's/\.+/_/'
I want to get A_Google_ but I get A_Google..
The sed 's/\.+/_/' part is obviously wrong.
BTW, sed 's/\%20/_/' and sed 's/%20/_/' both work. Which is better?
sed speaks POSIX basic regular expressions, which don't include + as a metacharacter. Portably, rewrite to use *:
sed 's/\.\.*/_/'
or if all you will ever care about is Linux, you can use various GNU-isms:
sed -r 's/\.\.*/_/' # turn on POSIX EREs (use -E instead of -r on OS X)
sed 's/\.\+/_/' # GNU regexes invert behavior when backslash added/removed
That last example answers your other question: a character which is literal when used as is may take on a special meaning when backslashed, and even though at the moment % doesn't have a special meaning when backslashed, future-proofing means not assuming that \% is safe.
Additional note: you don't need two separate sed commands in the pipeline there.
echo $name | sed -e 's/\%20/_/' -e 's/\.+/_/'
(Also, do you only need to do that once per line, or for all occurrences? You may want the /g modifier.)
The sed command doesn't understand + so you'll have to expand it by hand:
sed 's/\.\.*/_/'
Or tell sed that you want to use extended regexes:
sed -r 's/\.+/_/' # GNU
sed -E 's/\.+/_/' # OSX
Which switch, -r or -E, depends on your sed and it might not even support extended regexes so the portable solution is to use \.\.* in place of \.+. But, since you're on Linux, you should have GNU sed so sed -r should do the trick.