bash script on specific URL string manipulation - bash

I need to manipulate a string (URL) of which I don't know lenght.
the string is something like
https://x.xx.xxx.xxx/dontcare1/dontcare2/dontcareN/keyword/restofstring
I basically need a regular expression which returns this:
https://x.xx.xxx.xxx/keyword/restofstring
where the x is the current ip which can vary everytime and I don't know the number of dontcares.
I actually have no idea how to do it, been 2 hours on the problem but didn't find a solution.
thanks!

You can use sed as follows:
sed -E 's=(https://[^/]*).*(/keyword/.*)=\1\2='
s stands for substitute and has the form s=search pattern=replacement pattern=.
The search pattern is a regex in which we grouped (...) the parts you want to extract.
The replacement pattern accesses these groups with \1 and \2.
You can feed a file or stdin to sed and it will process the input line by line.
If you have a string variable and use bash, zsh, or something similar you also can feed that variable directly into stdin using <<<.
Example usage for bash:
input='https://x.xx.xxx.xxx/dontcare1/dontcare2/dontcareN/keyword/restofstring'
output="$(sed -E 's=(https://[^/]*).*(/keyword/.*)=\1\2=' <<< "$input")"
echo "$output" # prints https://x.xx.xxx.xxx/keyword/restofstring

echo "https://x.xx.xxx.xxx/dontcare1/dontcare2/dontcareN/keyword/restofstring" | sed "s/dontcare[0-9]\+\///g"
sed is used to manipulate text. dontcare[0-9]\+\///g is an escaped form of the regular expression dontcare[0-9]+/, which matches the word "dontcare" followed by 1 or more digits, followed by the / character.
sed's pattern works like this: s/find/replace/g, where g is a command that allowed you to match more than one instance of the pattern.
You can see that regular expression in action here.
Note that this assumes there are no dontcareNs in the rest of the string. If that's the case, Socowi's answer works better.

You could also use read with a / value for $IFS to parse out the trash.
$: IFS=/ read proto trash url trash trash trash keyword rest <<< "https://x.xx.xxx.xxx/dontcare1/dontcare2/dontcareN/keyword/restofstring"
$: echo "$proto//$url/$keyword/$rest"
https://x.xx.xxx.xxx/keyword/restofstring
This is more generalized when the dontcare... values aren't known and predictable strings.
This one is pure bash, though I like Socowi's answer better.

Here's a sed variation which picks out the host part and the last two components from the path.
url='http://example.com:1234/ick/poo/bar/quux/fnord'
newurl=$(echo "$url" | sed 's%\(https*://[^/?]*[^?/]\)[^ <>'"'"'"]*/\([^/ <>'"''"]*/^/ <>'"''"]*\)%\1\2%')
The general form is sed 's%pattern%replacement%' where the pattern matches through the end of the host name part (captured into one set of backslashed parentheses) then skips through the penultimate slash, then captures the remainder of the URL including the last slash; and the replacement simply recalls the two captured groups without the skipped part between them.

Related

Replacing variable section in string

I am having a long list of strings (actually files names) $var looking like this
p1035sEthinylestradiol913
p1035sTAbs872
p946sCarbaryl1182
Now I wish to replace the string, which occurs between the first s and the first integer [1-9], with R. Hence the output should look like:
p1035sR913
p1035sR872
p946sR1182
I was trying something like this:
echo ${var/s*[1-9]/R}
But this of course will remove the first integer in the string after the smatch and that is not what I want. Can someone help me out here? Thanks a lot in advance!
To keep the matched digit you could switch from parameter expansions like ${var/s*[1-9]/R} to matching [[ string =~ pattern ]]. The matched digit could then be retrieved by BASH_REMATCH. However, you still had to do this for every entry in your list.
With sed you automatically change every line and keeping the digit is easy:
sed -E 's/s.*([0-9])/sR\1/' file
or
someCommand | sed -E 's/s.*([0-9])/sR\1/'

Extract a section in a config file line using sed

I'm trying to continue to extract and isolate sections of text within my wordpress config file via bash script. Can someone help me figure out my sytax?
The lineof code in the wp-config.php file is:
$table_prefix = 'xyz_';
This is what I'm trying to use to extract the xyz_ portion.
prefix=$(sed -n "s/$table_prefix = *'[^']*'/p" wp-config.php)
echo -n "$prefix"
There's something wrong with my characters obviously. Any help would be much appreciated!
Your sed command is malformed. You can use s/regex/replacement/p to print your sed command. Yours, as written, will give unterminated 's' command. If you want to print your whole line out, you can use the capture group \0 to match it as s/<our_pattern>/\0/p
Bash interpets $table_prefix as a variable, and because it is in double quotes, it tries to expand it. Unless you set this variable to something, it expands to nothing. This would cause your sed command to match much more liberally, and we can fix it by escaping the $ as \$table_prefix.
Next, this won't actually match. Your line has multiple spaces before the =, so we need another wildcard there as in ...prefix *= *...
Lastly, to extract the xyz_ portion alone, we'll need to do some things. First, we have to make sure our pattern matches the whole line, so that when we substitute, the rest of the line won't be kept. We can do this by wrapping our pattern to match in ^.* ... .*\$. Next, we want to wrap the target section in a capture group. In sed, this is done with \(<stuff>\). The zeroth capture group is the whole line, and then capture groups are numbered in the order the parentheses appear. this means we can do \([^']*\) to grab that section, and \1 to output it:
All that gives us:
prefix=$(sed -n "s/^.*\$table_prefix *= *'\([^']*\)'.*\$/\1/p" wp-config.php)
The only issue with the regex is that the '$' character specifies that you are using a bash variable and since the pattern is wrapped in double quotes (", bash will attempt to expand the variable. You can mitigate this by either escapping the $ or wrapping the pattern in single quotes and escaping the single quotes in the pattern
Lastly, you are using the sed command s which stands for subsitute. It takes a pattern and replaces the matches with text in the form of s/<pattern>/<replace>/. You can omit the 's' and leave the 'p' or print command at the end. After all your command should look something like:
sed -n "/\$table_prefix = *'[^']*'/p" wp-config.php

Understanding sed command

Please excuse if the question is too naive. I am new to shell scripting and am not able to find any good resource to understand the specifics. I am trying to make sense of a legacy script. Please can someone tell me what the following command does:
sed "s#s3AtlasExtractName#$i#g" load_xyz.sql >> load_abc.sql;
This command will replace all occurrences of s3AtlasExtractName with whatever $i is.
s - Substitute
# - Delimiter
s3AtlasExtractName - Word that needs substituting
# - Delimiter
$i - i variable that will be used to replace s3AtlasExtractName
# - Delimiter
g - Global Replace all instance of s3AtlasExtractName in a single line and not just the first occurrence of it
So this will parse through load_xyz.sql and change all occurrences of s3AtlasExtractName to the value of $i and append the whole of the contents of load_xyz.sql to a file called load_abc.sql with the sed substitutions.
sed is a command line stream editor. You can find information about it here:
http://www.computerhope.com/unix/used.htm
An easy example is shown below where sed is used to replace the word "test" with the word "example" in myfile.txt but output is sent to newfile.txt
sed 's/test/example/g' myfile.txt > newfile.txt
It seems that your script is performing a similar function by replacing the content of the load_xyz.sql file and storing it in a new file load_abc.sql Without more code I am just guessing but it seems that the parameter $i could be used as counter to insert similar but new values into the load_abc.sql file.
In short, this reads load_xyz.sql and replaces every occurrence of "s3AtlasExtractName" by whatever has been stored in the shell variable "i".
The long version is that sed accepts many subcommands with different formattings. Any "simple" sed command will look like 'sed '. The first letter of the subcommand tells you which operation sed is going to do with your files.
The "s" operation stands for "substitution" and is the most commonly used. It is followed by a Perl-like regexp: separator, regexp to look for, separator, value to substitute, separator, PREG flags. In your case, the separator is '#' which is pretty unusual but not forbidden, so the command substitues '$i' to every instance of 's3AtlasExtractName'. The 'g' PREG flag tells sed to replace every occurrence of the pattern (the default is to only replace its first occurrence on every line in the input).
Finally, the use of "$i" inside a double-quote-delimited string tells the shell to actually expand the shell variable 'i' so you'll want to look for a shell statement setting that (possibly a 'for' statement).
Hope this helps.
edit: I focused on the 'sed' part and kinda missed the redirection part. The '>>' token tells the shell to take the output of the sed command (i.e. the contents of load_xyz.sql with all occurrences of s3AtlasExtractName replaced by the contents of $i) and append it to the file 'load_abc.sql'.

Extract parts of file path and concatenate in bash

I am new to bash scripting and my dir structure looks like below.
"/ABC/DEF/GHI/JKL/2015/01/01"
I am trying to produce the output like this - "JKL_2015-01-01".
I am trying using sed and cut and might take a while but this is needed immediately and any help is appreciated. Thanks.
i=/ABC/DEF/GHI/JKL/2015/01/01
o=`echo $i | sed -r 's|^.+/([^/]+)/([0-9]+)/([0-9]+)/([0-9]+)$|\1_\2-\3-\4|'`
i=xxx is a variable assignment, no whitespace around = allowed!
`command`
enclosed by backticks is a command substitution, which captures the standard output of the command inside as a string.
And sed is the stream editor, applying mostly regex based operations to each line from standard input, and emitting the result on standard output.
sed's s||| operation is regex based substitution. I capture 4 character groups with parens (): (non-slashes), slash, (numbers), slash, (numbers), slash, (numbers), end-of-string $. Then in the second part of the subst I print the for captured groups, separated by an underscore and 2 dashes, respectively.
There's no need to use tools that aren't built into bash for this -- using builtins is far more efficient than external tools like sed.
s="/ABC/DEF/GHI/JKL/2015/01/01"
s_re='/([^/]+)/([^/]+)/([^/]+)/([^/]+)$'
if [[ $s =~ $s_re ]]; then
name="${BASH_REMATCH[1]}_${BASH_REMATCH[2]}-${BASH_REMATCH[3]}-${BASH_REMATCH[4]}"
echo "$name"
fi
Alternately, and perhaps more readably (using string manipulation techniques documented in BashFAQ #100):
s="/ABC/DEF/GHI/JKL/2015/01/01"
s_prefix=${s%/*/*/*/*} # find the content we don't care about
s_suffix=${s#"$s_prefix"/} # strip that content
# read the rest into named variables
IFS=/ read -r category year month day <<<"$s_suffix"
# assemble those named variables into the string we care about
echo "${category}_${year}-${month}-${day}"

sed partial replace or variable

I'd like to use sed to do a replace, but not by searching for what to replace.
Allow me to explain. I have a variable set to a default value initially.
VARIABLE="DEFAULT"
I can do a sed to replace DEFAULT with what I want, but then I would have to put DEFAULT back when I was all done. This is becuase what gets stored to VARIABLE is unique to the user. I'd like to use sed to search for somthing else other than what to replace. For example, search for VARIABLE=" and " and replace whats between it. That way it just constantly updates and there is no need to reset VARIABLE.
This is how I do it currently:
I call the script and pass an argument
./script 123456789
Inside the script, this is what happens:
sed -i "s%DEFAULT%$1%" file_to_modify
This replaces
VARIABLE="DEFAULT"
with
VARIABLE="123456789"
It would be nice if I didn't have to search for "DEFAULT", because then I would not have to reset VARIABLE at end of script.
sed -r 's/VARIABLE="[^"]*"/VARIABLE="123456789"/' file_to_modify
Or, more generally:
sed -r 's/VARIABLE="[^"]*"/VARIABLE="'"$1"'"/' file_to_modify
Both of the above use a regular expression that looks for 'VARIABLE="anything-at-all"' and replaces it with, in the first example above 'VARIABLE="123456789"' or, in the second, 'VARIABLE="$1"' where "$1" is the first argument to your script. The key element is [^"]. It means any character other than double-quote. [^"]* means any number of characters other than double-quote. Thus, we replace whatever was in the double-quotes before, "[^"]*", with our new value "123456789" or, in the second case, "$1".
The second case is a bit tricky. We want to substitute $1 into the expression but the expression is itself in single quotes. Inside single-quotes, bash will not substitute for $1. So, the sed command is broken up into three parts:
# spaces added for exposition but don't try to use it this way
's/VARIABLE="[^"]*"/VARIABLE="' "$1" '"/'
The first part is in single quotes and bash passes it literally to sed. The second part is in double-quotes, so bash will subsitute in for the value of `$``. The third part is in single-quotes and gets passed to sed literally.
MORE: Here is a simple way to test this approach on the command line without depending on any files:
$ new=1234 ; echo 'VARIABLE="DEFAULT"' | sed -r 's/VARIABLE="[^"]*"/VARIABLE="'"$new"'"/'
VARIABLE="1234"
The first line above is the command run at the prompt ($). The second is the output from running the command..

Resources