I have the following SED command
echo "abcd_2222222233333333_jdkj" | sed -e 's/^\(.*\)_\(.*\)_\(.*\)$/\2_\1_\3/'
that returns
2222222233333333_abcd_jdkj
That's great, but I really want
22222222-33333333_abcd_jdkj
Is this possible with an easy tweak or do I need some non-sed solution? Basically, I know the number is 16 bytes, but I need to break it into two 8 byte numbers.
Instead of .* to match any number of characters, you can use .{8} to match exactly eight characters.
The below also uses sed -r to allow ERE syntax, which requires fewer backslashes and is generally easier to read than the default BRE. (On systems with BSD-style tools, this might be sed -E instead).
sed -re 's/^(.*)_(.{8})(.*)_(.*)$/\2-\3_\1_\4/' <<<"abcd_2222222233333333_jdkj"
By the way -- I would strongly suggest using [^_]* instead of .* so your regex can't match underscores where you don't want it to. (. means "any character"; [^_] means "any character except _"). That's not just a correctness enhancement -- it can also make your regex faster to evaluate by avoiding backtracking (where the regex engine realizes it's matched too much content and needs to undo some of its prior matches).
Also consider bash's built-in regex support:
string='abcd_2222222233333333_jdkj'
re='([^_]+)_([[:digit:]]{8})([[:digit:]]+)_(.*)'
if [[ $string =~ $re ]]; then
result=${BASH_REMATCH[2]}-${BASH_REMATCH[3]}_${BASH_REMATCH[1]}_${BASH_REMATCH[4]}
echo "Result is: $result"
else
echo "No match found"
fi
Solution per the above commenter's tip works
echo "abcd_2222222233333333_jdkj" | sed -e 's/^\(.*\)_\(.\{8\}\)\(.\{8\}\)_\(.*\)$/\2-\3_\1_\4/'
How to replace double consonants with only one letter using sed Linux command. Example: WILLIAM -> WILIAM. grep -E '(.)\1+' commands finds the words that follow two same consonants in a row pattern, but how do I replace them with only one occurrence of the letter?
I tried
cat test.txt | head | tr -s '[^AEUIO\n]' '?'
tr is all or nothing; it will replace all occurrences of the selected characters, regardless of context. For regex replacement, look at sed - you even included this in your question's tags, but you don't seem to have explored how it might be useful?
sed 's/\(.\)\1/\1/g' test.txt
The dot matches any character; to restrict to only consonants, change it to [b-df-hj-np-tv-xz] or whatever makes sense (maybe extend to include upper case; perhaps include accented characters?)
The regex dialect understood by sed is more like the one understood by grep without -E (hence all the backslashes); though some sed implementations also support this option to select the POSIX extended regular expression dialect.
Neither sed not tr need cat to read standard input for them (though tr obscurely does not accept a file name argument). See tangentially also Useless use of cat?
Match one consonant, remember it in \( \), then match is again with \1 and substitute it for itself.
sed 's/\([bcdfghjklmnpqrstvxzBCDFGHJKLMNPQRSTVXZ]\)\1/\1/'
How do I tell sed to repeat substitution until no match was replaced?
If doing echo x | sed 's/x/xx/g' I'm really glad sed doesn't restart on the output.
But if I have, say, echo 'x,a,b,x,x,c,x,d,e,x,x,x,f,x' | sed 's/,x,/,y,/g'
it does not substitute every x for y, for an obvious reason: the prior substitution has already consumed the surrounding delimiters.
And I'm aware that I have a tiny problem with the first and last x as well, but I ignore this for simplicity of the question.
Edit: I have to clarify the question, as already mentioned but only in comments: I want to see every x replaced by y, but only if it was a single word for itself, enclosed by delimiters, commas in this example, but if there is a way to cope with more complex delimiters, this will be welcome.
(No way to fall into the y2k trap, replacing Monday by Mondak, just joking.)
Use \b as a word delimiter.
$ echo 'x,xx,x,x' | sed 's/\bx\b/y/g'
y,xx,y,y
\b denotes word boundaries, but even used within a capture group it's not going to cause replacement of the characters outside the word, if any.
Try this:
$ echo 'x,a,b,x,x,c,x,d,e,x,x,x,f,x' | sed 's/x/y/g'
y,a,b,y,y,c,y,d,e,y,y,y,f,y
What about
$ echo 'x,a,b,x,x,c,x,d,e,x,x,x,f,x' | sed ':label; s/,x,/,y,/g; t label;'
x,a,b,y,y,c,y,d,e,y,y,y,f,x
? This will not replace the x at the edges but that was not requested explicitly.
It will also not replace x in words:
$ echo 'x,a,b,fix,x,c,x,d,e,x,x,x,f,x' | sed ':label; s/,x,/,y,/g; t label;'
x,a,b,fix,y,c,y,d,e,y,y,y,f,x
Explanation: the t command will jump to the label if some substition took place. It will the apply the same sed expression to the line again.
I am attempting to use the sqrt function from awk command in my script, but all it returns is 0. Is there anything wrong with my script below?
echo "enter number"
read root
awk 'BEGIN{ print sqrt($root) }'
This is my first time using the awk command, are there any mistakes that I am not understanding here?
Maybe you can try this.
echo "enter number"
read root
echo "$root" | awk '{print sqrt($0)}'
You have to give a data input to awk. So, you can pipe 'echo'.
The BEGIN statement is to do things, like print a header...etc before
awk starts reading the input.
$ echo "enter number"
enter number
$ read root
3
$ awk -v root="$root" 'BEGIN{ print sqrt(root) }'
1.73205
See the comp.unix.shell FAQ for the 2 correct ways to pass the value of a shell variable to an awk script.
UPDATE : My proposed solution turns out to be potentially dangerous. See Ed Morton's answer for a better solution. I'll leave this answer here as a warning.
Because of the single quotes, $root is interpreted by awk, not by the shell. awk treats root as an uninitialized variable, whose value is the empty string, treated as 0 in a numeric context. $root is the root'th field of the current line -- in this case, as $0, which is the entire line. Since it's in a BEGIN block, there is no current line, so $root is the empty string -- which again is treated as 0 when passed to sqrt().
You can see this by changing your command line a bit:
$ awk 'BEGIN { print sqrt("") }'
0
$ echo 2 | awk '{ print sqrt($root) }'
1.41421
NOTE: The above is merely to show what's wrong with the original command, and how it's interpreted by the shell and by awk.
One solution is to use double quotes rather than single quotes. The shell expands variable references within double quotes:
$ echo "enter number"
enter number
$ read x
2
$ awk "BEGIN { print sqrt($x) }" # DANGEROUS
1.41421
You'll need to be careful when doing this kind of thing. The interaction between quoting and variable expansion in the shell vs. awk can be complicated.
UPDATE: In fact, you need to be extremely careful. As Ed Morton points out in a comment, this method can result in arbitrary code execution given a malicious value for $x, which is always a risk for a value read from user input. His answer avoids that problem.
(Note that I've changed the name of your shell variable from $root to $x, since it's the number whose square root you want, not the root itself.)
I have a file where a few lines end with tux. How do I add " to the end of any line that ends in words like this or This?
You could visit this site for more examples and help about using sed in overall. Also check it's "Regular expressions" tab or search the web for something like "unix anchor characters".
For this actual problem, these are the relevant parts of the site:
Sed has the ability to specify which lines are to be examined and/or modified, by specifying addresses before the command. I will just describe the simplest version for now - the /PATTERN/ address. When used, only lines that match the pattern are given the command after the address. Briefly, when used with the /p flag, matching lines are printed twice:
sed '/PATTERN/p' file
And of course PATTERN is any regular expression.
According to these, you could use a sed command like this to get the lines ending with "this" or "This" in your file, or "tux" if you meant that:
$ sed '/[tT]his$/p' yourfile
or
$ sed '/tux$/p' yourfile
For putting the double quotes at the end of these lines, you also need to understand:
$ has a special meaning (end of the input line) as an anchor character in regular expressions
... and the character "$" is the end anchor. The expression "A$" will match all lines that end with the capital A. If the anchor characters are not used at the proper end of the pattern, then they no longer act as anchors. The "$" is only an anchor if it is the last character.
how to use sed for substitution of characters (see the linked page)
Sed has several commands, but most people only learn the substitute command: s. The substitute command changes all occurrences of the regular expression into a new value. A simple example is changing "day" in the "old" file to "night" in the "new" file:
$ sed 's/day/night/' newfile
Or another way (for UNIX beginners),
$ sed 's/day/night/' old >new
and for those who want to test this:
$ echo day | sed 's/day/night/'
This will output "night".
After these you can construct your own sed command, knowing that you can use this two parts together in one command like this:
$ sed '/[pP]atternAtTheEndOfLine$/s/$/patternToAddToEndOfTheLine/' yourfile