I'm trying to use sed as root to alter the default PS1.
The first 2 lines were just to make sure I had the syntax structured right and to see if the quotation marks made a difference,
running them consecutively allows me to change a comment near the top of the file and then change it back.
Opening the file in nano confirms the changes are effective, which should rule out 'write permissions'.
sed -i 's/If not running interactively,/stringtoreplaceitwith/' /etc/skel/.bashrc
sed -i "s/stringtoreplaceitwith/If not running interactively,/" /etc/skel/.bashrc
sed -i "s/\[\033[01;32m\]\u#\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ /Replace PS1/" /etc/skel/.bashrc
I'm not sure if it's something else about the string's structure,
but for some reason, it's not finding what I'd like to substitute.
\[\033[01;32m\]\u#\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$
(with a trailing blank).
Your problem is due to quoting and escaping. Let's reduce the string you're trying to substitute to just this:
\w\[\033[00m\]\$
(with a trailing blank) – this contains all the difficulties, but is less verbose.
To match this, we have to
escape all the backslashes: \w becomes \\w etc.
escape [ and ], because they're special to sed: [ becomes \[, and \[ becomes \\\[ (escaped backslash, escaped [)
escape $: \$ becomes \\\$
Then, we have to use single quotes around our sed command so the shell doesn't modify the string:
$ sed 's/\\w\\\[\\033\[00m\\\]\\\$ /Replace PS1/' <<< '\w\[\033[00m\]\$ '
Replace PS1
It can also work with double quotes, but then we have to add another round of escaping for the shell: \[ becomes \\\[ (escaped for sed) becomes \\\\\\[ (escaped for the shell), and so on.
$ sed "s/\\\\w\\\\\\[\\\\033\\[00m\\\\\\]\\\\\\$ /Replace PS1/" <<< '\w\[\033[00m\]\$ '
Replace PS1
Double quoting only makes sense if you're using variables, though, for obvious reasons.
Finally, for your actual string:
$ echo '\[\033[01;32m\]\u#\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ ' \
| sed 's/\\\[\\033\[01;32m\\\]\\u#\\h\\\[\\033\[00m\\\]:\\\[\\033\[01;34m\\\]\\w\\\[\\033\[00m\\\]\\\$ /Replace PS1/'
Replace PS1
Related
this is perhaps one of the most discussed topics here. I tried almost all the commands and other tweaks found here, but something doesn't seems to be doing well.
i would want to replace all the double quotes in my file with whitespace/blank
I'm seeing the below error when i tried to execute this command.
sed "s/"/ \''/g' x_orbit.txt > new.tx
sed: -e expression #1, char 3: unterminated `s' command
You're close. Just use single quotes, so the shell doesn't try to expand the metacharacters in your sed command:
sed 's/"/ /g' x_orbit.txt > new.txt
You could try tr for example:
tr '"' ' ' < x_orbit.txt > new.txt
The script you provided:
sed "s/"/ \''/g' x_orbit.txt > new.tx
means:
sed # invoke sed to execute the following script:
" # enclose the script in double quotes rather than single so the shell can
# interpret it (e.g. to expand variables like $HOME) before sed gets to
# interpret the result of that expansion
s/ # replace what follows until the next /
" # exit the double quotes so the shell can now not only expand variables
# but can now do globbing and file name expansion on wildcards like foo*
/ # end the definition of the regexp you want to replace so it is null since
# after the shell expansion there was no text for sed to read between
# this / and the previous one (the 2 regexp delimiters)
\' # provide a blank then an escaped single quote for the shell to interpret for some reason
'/g' # enclose the /g in single quotes as all scripts should be quoted by default.
That is so far off the correct syntax it's kinda shocking which is why I dissected it above to try to help you understand what you wrote so you'll see why it doesn't work. Where did you get the idea to write it that way (or to put it another way - what did you think each character in that script meant? I'm asking as it indicates a fundamental misunderstanding of how quoting and escaping works in shell so it'd be good if we could help correct that misunderstanding rather than just correct that script.
When you use any script or string in shell, simply always enclose it in single quotes:
sed 'script' file
var='string'
unless you NEED to use double quotes to let a variable expand and then use double quotes unless you NEED to use no quotes to let globbing and file name expansion happen.
An awk version:
awk '{gsub(/"/," ")}1' file
gsub is used for the replace
1 is always true, so line is printed
I am attempting to use (BSD) sed to modify my /etc/gettytab. The goal is to modify this entry:
P|Pc|Pc console:\
:ht:np:sp#9600:
to this entry:
P|Pc|Pc console:\
:ht:np:sp#115200:\
:cl=\E[H\E[2J:
If I issue the command below (it's on two lines), it works perfectly.
# sed -in ' /P|Pc|Pc console/,/^#/ s/9600:/115200:\\\\
:cl=\E[H\E[2J:/' /etc/gettytab
However, if I use the exact same command (literally copy/paste it) in a script, I get an error message:
sed: 1: " /P|Pc|Pc console/,/^#/ ...": unescaped newline inside substitute pattern
Searching, I found this post: unescaped newline inside substitute pattern which talks about the trailing /, but I have that in my pattern.
If anyone can assist with what I am doing wrong, I would greatly appreciate it.
Within your script, you escape newlines with a \, and you escape the \ that you're embedding into your output so that it will be interpreted literally. If my math is right, that comes to THREE, not four backslashes.
$ cat i
P|Pc|Pc console:\
:ht:np:sp#9600:
$ cat i.sh
#!/bin/sh
# ┏━━━ escapes the next character,
# ┃┏━━ literal backslash for output,
# ┃┃┏━ escapes the newline.
sed -ne '/^P|/,/^#/ s/9600:/115200:\\\
:cl=\E[H\E[2J:/' -e p i
$ ./i.sh
P|Pc|Pc console:\
:ht:np:sp#115200:\
:cl=E[HE[2J:
$
I am on Mac OS X and using sed for an in-place replacement.
Essentially I have this:
#!/bin/sh -e
PREFIX="$1"
sed -i bak -e 's|OCAMLDIR|"${PREFIX}"|g' ocamloptrev
Where PREFIX is a path, hence I'm using the |.
Unfortunately, the variable in the file path is not getting evaluated as I expected, I end up with:
OCAMLC="${PREFIX}"/bin/ocamlopt
How can I get the right evaluation of ${PREFIX} into the sed command?
Try this:
#!/bin/sh -e
PREFIX="$1"
sed -i bak -e 's|OCAMLDIR|'"${PREFIX}"'|g' ocamloptrev
What you're basically doing, is "exiting"/getting outside the single-quoted string, entering into a double-quoted string, interpreting the variable inside double-quotes, and then entering the single quotes again.
With this simple example, we could also just use double-quotes, which allow variables to be interpreted:
#!/bin/sh -e
PREFIX="$1"
sed -i bak -e "s|OCAMLDIR|${PREFIX}|g" ocamloptrev
If you try to use double-quotes ("") inside single-quotes, they don't get interpreted either. This part of the Bash manual explains this in more detail.
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). ...
Shell variables are not expanded inside single quotes (there are no metacharacters within single quotes, not even backslashes), so you need to use something like this, with the double quotes around ${PREFIX} ensuring that spaces etc in the value are handled correctly:
sed -i bak -e 's|OCAMLDIR|'"${PREFIX}"'|g' ocamloptrev
Or you could even use:
sed -i bak -e "s|OCAMLDIR|${PREFIX}|g" ocamloptrev
The latter is safe because the material inside the double quotes does not contain shell metacharacters (dollar signs, backslashes and back-quotes are the main danger signs). If there were dodgy characters in the rest of the string, the first version is safer to use.
Personally, I'd use .bak rather than just bak as the suffix.
I have file with comments like this:
\$max_servers = 2;
\#\## BLOCKED ANYWHERE
I'm trying to
Replace all instances of \$ with $.
Replace all instances of \#\## with ###.
I wonder how I can go about doing that via sed or awk
What I have tried so far without much success using vi or vim
%s/^\//gc
%s/^#/\\/###/gc
Thank you
Another option to replace all [#$] in one pass is to use the following regular expression. The following is VI syntax:
:%s/\\\([$#]\)/\1/g
Replace the characters in the brackets [] with whatever you need if its more than just # and $.
The first \\ is a backslash - escaped since its inside a regular expression
The expression between the \( and \) is saved and later used in the replacement as \1.
Escaping backslash will work
#echo "\#\##"| sed "s/\\\\#\\\\##/###/g"
###
# echo "\\$"| sed "s/\\\\\\$/$/g"
$
In order to replace a backslash, you have to double it up, so it can quote itself much the way other special characters must be quoted. You can use sed instead of vim to help automate the process a bit:
$ sed -e 's/^\\\$/$/' -e 's/^\\#\\##/###/' $file > $new_file
Note that you have to put a backslash in front of dollar signs since they are used to mark an end of line in regular expressions. That's why I have \\\$ in my first expression. One backslash to quote the backslash and another backslash to quote the dollar sign.
By the way, these same sed expressions will also work inside Vim depending upon your Vim settings.
You escape special characters with the backslash. So for example, to replace everything with \$, you would do
%s/\\\$/$/g
sed 's|^\\\([$#]\)\\\{0,1\}|\1|' YourFile
work for your sample bu will also remove the 2 \ in \$\ ...,
In the below shell script I try to print A2D(Vlog-Ams-#Cross) with special characters escaped. For example replace ( with \( but sed won't have any effect.
#! /bin/sh
parameter="A2D(Vlog-Ams-#Cross)"
echo $parameter
parameterz=`echo "$parameter" | sed 's/(/\\(/g'`
echo $parameterz
The output is
A2D(Vlog-Ams-#Cross)
A2D(Vlog-Ams-#Cross)
If I do the same on my c-shell terminal, it works fine.
Any ideas?
You use backslashs within a backtick command and that's tricky. If the sed command didn't occur within backticks, it would work correctly. When the shell looks for the closing backtick, however, it removes one level of backslash quoting, so you get
sed 's/(/\(/g'
and that's a no-op. If your shell permits it, use $(...) instead of backticks; in this way you avoid these quoting problems.
In your replacement \\( the first \ escapes the second \. But you must escape the (, too:
$ echo 'A2D(Vlog-Ams-#Cross)' | sed -e 's/(/\\\(/g' -e 's/)/\\\)/g'
A2D\(Vlog-Ams-#Cross\)