Related
Suppose echo $PATH yields /first/dir:/second/dir:/third/dir.
Question: How does one echo the contents of $PATH one directory at a time as in:
$ newcommand $PATH
/first/dir
/second/dir
/third/dir
Preferably, I'm trying to figure out how to do this with a for loop that issues one instance of echo per instance of a directory in $PATH.
echo "$PATH" | tr ':' '\n'
Should do the trick. This will simply take the output of echo "$PATH" and replaces any colon with a newline delimiter.
Note that the quotation marks around $PATH prevents the collapsing of multiple successive spaces in the output of $PATH while still outputting the content of the variable.
As an additional option (and in case you need the entries in an array for some other purpose) you can do this with a custom IFS and read -a:
IFS=: read -r -a patharr <<<"$PATH"
printf %s\\n "${patharr[#]}"
Or since the question asks for a version with a for loop:
for dir in "${patharr[#]}"; do
echo "$dir"
done
How about this:
echo "$PATH" | sed -e 's/:/\n/g'
(See sed's s command; sed -e 'y/:/\n/' will also work, and is equivalent to the tr ":" "\n" from some other answers.)
It's preferable not to complicate things unless absolutely necessary: a for loop is not needed here. There are other ways to execute a command for each entry in the list, more in line with the Unix Philosophy:
This is the Unix philosophy: Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface.
such as:
echo "$PATH" | sed -e 's/:/\n/g' | xargs -n 1 echo
This is functionally equivalent to a for-loop iterating over the PATH elements, executing that last echo command for each element. The -n 1 tells xargs to supply only 1 argument to it's command; without it we would get the same output as echo "$PATH" | sed -e 'y/:/ /'.
Since this uses xargs, which has built-in support to split the input, and echoes the input if no command is given, we can write that as:
echo -n "$PATH" | xargs -d ':' -n 1
The -d ':' tells xargs to use : to separate it's input rather than a newline, and the -n tells /bin/echo to not write a newline, otherwise we end up with a blank trailing line.
here is another shorter one:
echo -e ${PATH//:/\\n}
You can use tr (translate) to replace the colons (:) with newlines (\n), and then iterate over that in a for loop.
directories=$(echo $PATH | tr ":" "\n")
for directory in $directories
do
echo $directory
done
My idea is to use echo and awk.
echo $PATH | awk 'BEGIN {FS=":"} {for (i=0; i<=NF; i++) print $i}'
EDIT
This command is better than my former idea.
echo "$PATH" | awk 'BEGIN {FS=":"; OFS="\n"} {$1=$1; print $0}'
If you can guarantee that PATH does not contain embedded spaces, you can:
for dir in ${PATH//:/ }; do
echo $dir
done
If there are embedded spaces, this will fail badly.
# preserve the existing internal field separator
OLD_IFS=${IFS}
# define the internal field separator to be a colon
IFS=":"
# do what you need to do with $PATH
for DIRECTORY in ${PATH}
do
echo ${DIRECTORY}
done
# restore the original internal field separator
IFS=${OLD_IFS}
I have a CSV file with this lines:
----------+79975532211,----------+79975532212
4995876655,4995876658
I try to grep this lines in Bash script
#!/bin/bash
config='/test/config.conf'
sourcecsv=/test/sourse.csv
cat $sourcecsv | while read line
do
Oldnumber=$(echo $line | cut -d',' -f1)
cat $config | grep "\\$Oldnumber" -B 8
done
But when script grep value 4995876655 I get error:
grep: Invalid back reference
How I can grep all values in my file?
Instead of:
cat $config | grep "\\$Oldnumber" -B 8
You should do:
grep -B 8 -F -- "$Oldnumber" "$config"
If you really mean to grep for all strings between commas, you can do it all in one go.
tr ',' '\n' </test/sourse.csv |
grep -F -f - -B 8 /test/config.conf
If you need to obtain the matches in sequence (all matches for the first string followed by all matches for the second, etc) then maybe loop over them with a proper while loop:
tr ',' '\n' </test/sourse.csv |
while read -r Oldnumber; do
grep -F -B 8 -e "$Oldnumber" /test/config.conf
done
Keeping the file names in variables does not seem to offer any advantage here.
If you mean to search for the strings preceded by a literal backslash, you can add it back; the -F option I added turns all strings into literals. If you need metacharacters, and take out the -F option, you need to double the backslashes (inside double quotes, a single backslash needs to be represented as double; and to get a literal backslash in a regular expression, you need two of them).
I have a file containing a list of replacement pairs (about 100 of them) which are used by sed to replace strings in files.
The pairs go like:
old|new
tobereplaced|replacement
(stuffiwant).*(too)|\1\2
and my current code is:
cat replacement_list | while read i
do
old=$(echo "$i" | awk -F'|' '{print $1}') #due to the need for extended regex
new=$(echo "$i" | awk -F'|' '{print $2}')
sed -r "s/`echo "$old"`/`echo "$new"`/g" -i file
done
I cannot help but think that there is a more optimal way of performing the replacements. I tried turning the loop around to run through lines of the file first but that turned out to be much more expensive.
Are there any other ways of speeding up this script?
EDIT
Thanks for all the quick responses. Let me try out the various suggestions before choosing an answer.
One thing to clear up: I also need subexpressions/groups functionality. For example, one replacement I might need is:
([0-9])U|\10 #the extra brackets and escapes were required for my original code
Some details on the improvements (to be updated):
Method: processing time
Original script: 0.85s
cut instead of awk: 0.71s
anubhava's method: 0.18s
chthonicdaemon's method: 0.01s
You can use sed to produce correctly -formatted sed input:
sed -e 's/^/s|/; s/$/|g/' replacement_list | sed -r -f - file
I recently benchmarked various string replacement methods, among them a custom program, sed -e, perl -lnpe and an probably not that widely known MySQL command line utility, replace. replace being optimized for string replacements was almost an order of magnitude faster than sed. The results looked something like this (slowest first):
custom program > sed > LANG=C sed > perl > LANG=C perl > replace
If you want performance, use replace. To have it available on your system, you'll need to install some MySQL distribution, though.
From replace.c:
Replace strings in textfile
This program replaces strings in files or from stdin to stdout. It accepts a list of from-string/to-string pairs and replaces each occurrence of a from-string with the corresponding to-string. The first occurrence of a found string is matched. If there is more than one possibility for the string to replace, longer matches are preferred before shorter matches.
...
The programs make a DFA-state-machine of the strings and the speed isn't dependent on the count of replace-strings (only of the number of replaces). A line is assumed ending with \n or \0. There are no limit exept memory on length of strings.
More on sed. You can utilize multiple cores with sed, by splitting your replacements into #cpus groups and then pipe them through sed commands, something like this:
$ sed -e 's/A/B/g; ...' file.txt | \
sed -e 's/B/C/g; ...' | \
sed -e 's/C/D/g; ...' | \
sed -e 's/D/E/g; ...' > out
Also, if you use sed or perl and your system has an UTF-8 setup, then it also boosts performance to place a LANG=C in front of the commands:
$ LANG=C sed ...
You can cut down unnecessary awk invocations and use BASH to break name-value pairs:
while IFS='|' read -r old new; do
# echo "$old :: $new"
sed -i "s~$old~$new~g" file
done < replacement_list
IFS='|' will give enable read to populate name-value in 2 different shell variables old and new.
This is assuming ~ is not present in your name-value pairs. If that is not the case then feel free to use an alternate sed delimiter.
Here is what I would try:
store your sed search-replace pair in a Bash array like ;
build your sed command based on this array using parameter expansion
run command.
patterns=(
old new
tobereplaced replacement
)
pattern_count=${#patterns[*]} # number of pattern
sedArgs=() # will hold the list of sed arguments
for (( i=0 ; i<$pattern_count ; i=i+2 )); do # don't need to loop on the replacement…
search=${patterns[i]};
replace=${patterns[i+1]}; # … here we got the replacement part
sedArgs+=" -e s/$search/$replace/g"
done
sed ${sedArgs[#]} file
This result in this command:
sed -e s/old/new/g -e s/tobereplaced/replacement/g file
You can try this.
pattern=''
cat replacement_list | while read i
do
old=$(echo "$i" | awk -F'|' '{print $1}') #due to the need for extended regex
new=$(echo "$i" | awk -F'|' '{print $2}')
pattern=${pattern}"s/${old}/${new}/g;"
done
sed -r ${pattern} -i file
This will run the sed command only once on the file with all the replacements. You may also want to replace awk with cut. cut may be more optimized then awk, though I am not sure about that.
old=`echo $i | cut -d"|" -f1`
new=`echo $i | cut -d"|" -f2`
You might want to do the whole thing in awk:
awk -F\| 'NR==FNR{old[++n]=$1;new[n]=$2;next}{for(i=1;i<=n;++i)gsub(old[i],new[i])}1' replacement_list file
Build up a list of old and new words from the first file. The next ensures that the rest of the script isn't run on the first file. For the second file, loop through the list of replacements and perform them each one by one. The 1 at the end means that the line is printed.
{ cat replacement_list;echo "-End-"; cat YourFile; } | sed -n '1,/-End-/ s/$/³/;1h;1!H;$ {g
t again
:again
/^-End-³\n/ {s///;b done
}
s/^\([^|]*\)|\([^³]*\)³\(\n\)\(.*\)\1/\1|\2³\3\4\2/
t again
s/^[^³]*³\n//
t again
:done
p
}'
More for fun to code via sed. Try maybe for a time perfomance because this start only 1 sed that is recursif.
for posix sed (so --posix with GNU sed)
explaination
copy replacement list in front of file content with a delimiter (for line with ³ and for list with -End-) for an easier sed handling (hard to use \n in class character in posix sed.
place all line in buffer (add the delimiter of line for replacement list and -End- before)
if this is -End-³, remove the line and go to final print
replace each first pattern (group 1) found in text by second patttern (group 2)
if found, restart (t again)
remove first line
restart process (t again). T is needed because b does not reset the test and next t is always true.
Thanks to #miku above;
I have a 100MB file with a list of 80k replacement-strings.
I tried various combinations of sed's sequentially or parallel, but didn't see throughputs getting shorter than about a 20-hour runtime.
Instead I put my list into a sequence of scripts like "cat in | replace aold anew bold bnew cold cnew ... > out ; rm in ; mv out in".
I randomly picked 1000 replacements per file, so it all went like this:
# first, split my replace-list into manageable chunks (89 files in this case)
split -a 4 -l 1000 80kReplacePairs rep_
# next, make a 'replace' script out of each chunk
for F in rep_* ; do \
echo "create and make executable a scriptfile" ; \
echo '#!/bin/sh' > run_$F.sh ; chmod +x run_$F.sh ; \
echo "for each chunk-file line, strip line-ends," ; \
echo "then with sed, turn '{long list}' into 'cat in | {long list}' > out" ; \
cat $F | tr '\n' ' ' | sed 's/^/cat in | replace /;s/$/ > out/' >> run_$F.sh ;
echo "and append commands to switch in and out files, for next script" ; \
echo -e " && \\\\ \nrm in && mv out in\n" >> run_$F.sh ; \
done
# put all the replace-scripts in sequence into a main script
ls ./run_rep_aa* > allrun.sh
# make it executable
chmod +x allrun.sh
# run it
nohup ./allrun.sh &
.. which ran in under 5 mins, a lot less than 20 hours !
Looking back, I could have used more pairs per script, by finding how many lines would make up the limit.
xargs --show-limits </dev/null 2>&1 | grep --color=always "actually use:"
Maximum length of command we could actually use: 2090490
So just under 2MB; how many pairs would that be for my script ?
head -c 2090490 80kReplacePairs | wc -l
76923
So it seems I could have used 2 * 40000-line chunks
to expand on chthonicdaemon's solution
live demo
#! /bin/sh
# build regex from text file
REGEX_FILE=some-patch.regex.diff
# test
# set these with "export key=val"
SOME_VAR_NAME=hello
ANOTHER_VAR_NAME=world
escape_b() {
echo "$1" | sed 's,/,\\/,g'
}
regex="$(
(echo; cat "$REGEX_FILE"; echo) \
| perl -p -0 -e '
s/\n#[^\n]*/\n/g;
s/\(\(SOME_VAR_NAME\)\)/'"$(escape_b "$SOME_VAR_NAME")"'/g;
s/\(\(ANOTHER_VAR_NAME\)\)/'"$(escape_b "$ANOTHER_VAR_NAME")"'/g;
s/([^\n])\//\1\\\//g;
s/\n-([^\n]+)\n\+([^\n]*)(?:\n\/([^\n]+))?\n/s\/\1\/\2\/\3;\n/g;
'
)"
echo "regex:"; echo "$regex" # debug
exec perl -00 -p -i -e "$regex" "$#"
prefixing lines with -+/ allows empty "plus" values, and protects leading whitespace from buggy text editors
sample input: some-patch.regex.diff
# file format is similar to diff/patch
# this is a comment
# replace all "a/a" with "b/b"
-a/a
+b/b
/g
-a1|a2
+b1|b2
/sg
# this is another comment
-(a1).*(a2)
+b\1b\2b
-a\na\na
+b
-a1-((SOME_VAR_NAME))-a2
+b1-((ANOTHER_VAR_NAME))-b2
sample output
s/a\/a/b\/b/g;
s/a1|a2/b1|b2/;;
s/(a1).*(a2)/b\1b\2b/;
s/a\na\na/b/;
s/a1-hello-a2/b1-world-b2/;
this regex format is compatible with sed and perl
since miku mentioned mysql replace:
replacing fixed strings with regex is non-trivial,
since you must escape all regex chars,
but you also must handle backslash escapes ...
naive escaper:
echo '\(\n' | perl -p -e 's/([.+*?()\[\]])/\\\1/g'
\\(\n
How can I join multiple lines into one line, with a separator where the new-line characters were, and avoiding a trailing separator and, optionally, ignoring empty lines?
Example. Consider a text file, foo.txt, with three lines:
foo
bar
baz
The desired output is:
foo,bar,baz
The command I'm using now:
tr '\n' ',' <foo.txt |sed 's/,$//g'
Ideally it would be something like this:
cat foo.txt |join ,
What's:
the most portable, concise, readable way.
the most concise way using non-standard unix tools.
Of course I could write something, or just use an alias. But I'm interested to know the options.
Perhaps a little surprisingly, paste is a good way to do this:
paste -s -d","
This won't deal with the empty lines you mentioned. For that, pipe your text through grep, first:
grep -v '^$' | paste -s -d"," -
This sed one-line should work -
sed -e :a -e 'N;s/\n/,/;ba' file
Test:
[jaypal:~/Temp] cat file
foo
bar
baz
[jaypal:~/Temp] sed -e :a -e 'N;s/\n/,/;ba' file
foo,bar,baz
To handle empty lines, you can remove the empty lines and pipe it to the above one-liner.
sed -e '/^$/d' file | sed -e :a -e 'N;s/\n/,/;ba'
How about to use xargs?
for your case
$ cat foo.txt | sed 's/$/, /' | xargs
Be careful about the limit length of input of xargs command. (This means very long input file cannot be handled by this.)
Perl:
cat data.txt | perl -pe 'if(!eof){chomp;$_.=","}'
or yet shorter and faster, surprisingly:
cat data.txt | perl -pe 'if(!eof){s/\n/,/}'
or, if you want:
cat data.txt | perl -pe 's/\n/,/ unless eof'
Just for fun, here's an all-builtins solution
IFS=$'\n' read -r -d '' -a data < foo.txt ; ( IFS=, ; echo "${data[*]}" ; )
You can use printf instead of echo if the trailing newline is a problem.
This works by setting IFS, the delimiters that read will split on, to just newline and not other whitespace, then telling read to not stop reading until it reaches a nul, instead of the newline it usually uses, and to add each item read into the array (-a) data. Then, in a subshell so as not to clobber the IFS of the interactive shell, we set IFS to , and expand the array with *, which delimits each item in the array with the first character in IFS
I needed to accomplish something similar, printing a comma-separated list of fields from a file, and was happy with piping STDOUT to xargs and ruby, like so:
cat data.txt | cut -f 16 -d ' ' | grep -o "\d\+" | xargs ruby -e "puts ARGV.join(', ')"
I had a log file where some data was broken into multiple lines. When this occurred, the last character of the first line was the semi-colon (;). I joined these lines by using the following commands:
for LINE in 'cat $FILE | tr -s " " "|"'
do
if [ $(echo $LINE | egrep ";$") ]
then
echo "$LINE\c" | tr -s "|" " " >> $MYFILE
else
echo "$LINE" | tr -s "|" " " >> $MYFILE
fi
done
The result is a file where lines that were split in the log file were one line in my new file.
Simple way to join the lines with space in-place using ex (also ignoring blank lines), use:
ex +%j -cwq foo.txt
If you want to print the results to the standard output, try:
ex +%j +%p -scq! foo.txt
To join lines without spaces, use +%j! instead of +%j.
To use different delimiter, it's a bit more tricky:
ex +"g/^$/d" +"%s/\n/_/e" +%p -scq! foo.txt
where g/^$/d (or v/\S/d) removes blank lines and s/\n/_/ is substitution which basically works the same as using sed, but for all lines (%). When parsing is done, print the buffer (%p). And finally -cq! executing vi q! command, which basically quits without saving (-s is to silence the output).
Please note that ex is equivalent to vi -e.
This method is quite portable as most of the Linux/Unix are shipped with ex/vi by default. And it's more compatible than using sed where in-place parameter (-i) is not standard extension and utility it-self is more stream oriented, therefore it's not so portable.
POSIX shell:
( set -- $(cat foo.txt) ; IFS=+ ; printf '%s\n' "$*" )
My answer is:
awk '{printf "%s", ","$0}' foo.txt
printf is enough. We don't need -F"\n" to change field separator.
Suppose I have some output from a command (such as ls -1):
a
b
c
d
e
...
I want to apply a command (say echo) to each one, in turn. E.g.
echo a
echo b
echo c
echo d
echo e
...
What's the easiest way to do that in bash?
It's probably easiest to use xargs. In your case:
ls -1 | xargs -L1 echo
The -L flag ensures the input is read properly. From the man page of xargs:
-L number
Call utility for every number non-empty lines read.
A line ending with a space continues to the next non-empty line. [...]
You can use a basic prepend operation on each line:
ls -1 | while read line ; do echo $line ; done
Or you can pipe the output to sed for more complex operations:
ls -1 | sed 's/^\(.*\)$/echo \1/'
for s in `cmd`; do echo $s; done
If cmd has a large output:
cmd | xargs -L1 echo
You can use a for loop:
for file in * ; do
echo "$file"
done
Note that if the command in question accepts multiple arguments, then using xargs is almost always more efficient as it only has to spawn the utility in question once instead of multiple times.
You actually can use sed to do it, provided it is GNU sed.
... | sed 's/match/command \0/e'
How it works:
Substitute match with command match
On substitution execute command
Replace substituted line with command output.
A solution that works with filenames that have spaces in them, is:
ls -1 | xargs -I %s echo %s
The following is equivalent, but has a clearer divide between the precursor and what you actually want to do:
ls -1 | xargs -I %s -- echo %s
Where echo is whatever it is you want to run, and the subsequent %s is the filename.
Thanks to Chris Jester-Young's answer on a duplicate question.
xargs fails with with backslashes, quotes. It needs to be something like
ls -1 |tr \\n \\0 |xargs -0 -iTHIS echo "THIS is a file."
xargs -0 option:
-0, --null
Input items are terminated by a null character instead of by whitespace, and the quotes and backslash are
not special (every character is taken literally). Disables the end of file string, which is treated like
any other argument. Useful when input items might contain white space, quote marks, or backslashes. The
GNU find -print0 option produces input suitable for this mode.
ls -1 terminates the items with newline characters, so tr translates them into null characters.
This approach is about 50 times slower than iterating manually with for ... (see Michael Aaron Safyans answer) (3.55s vs. 0.066s). But for other input commands like locate, find, reading from a file (tr \\n \\0 <file) or similar, you have to work with xargs like this.
i like to use gawk for running multiple commands on a list, for instance
ls -l | gawk '{system("/path/to/cmd.sh "$1)}'
however the escaping of the escapable characters can get a little hairy.
Better result for me:
ls -1 | xargs -L1 -d "\n" CMD