I've got a script that calls grep to process a text file. Currently I am doing something like this.
$ grep 'SomeRegEx' myfile.txt > myfile.txt.temp
$ mv myfile.txt.temp myfile.txt
I'm wondering if there is any way to do in-place processing, as in store the results to the same original file without having to create a temporary file and then replace the original with the temp file when processing is done.
Of course I welcome comments as to why this should or should not be done, but I'm mainly interested in whether it can be done. In this example I'm using grep, but I'm interested about Unix tools in general. Thanks!
sponge (in moreutils package in Debian/Ubuntu) reads input till EOF and writes it into file, so you can grep file and write it back to itself.
Like this:
grep 'pattern' file | sponge file
Perl has the -i switch, so does sed and Ruby
sed -i.bak -n '/SomeRegex/p' file
ruby -i.bak -ne 'print if /SomeRegex/' file
But note that all it ever does is creating "temp" files at the back end which you think you don't see, that's all.
Other ways, besides grep
awk
awk '/someRegex/' file > t && mv t file
bash
while read -r line;do case "$line" in *someregex*) echo "$line";;esac;done <file > t && mv t file
No, in general it can't be done in Unix like this. You can only create/truncate (with >) or append to a file (with >>). Once truncated, the old contents would be lost.
In general, this can't be done. But Perl has the -i switch:
perl -i -ne 'print if /SomeRegEx/' myfile.txt
Writing -i.bak will cause the original to be saved in myfile.txt.bak.
(Of course internally, Perl just does basically what you're already doing -- there's no special magic involved.)
To edit file in-place using vim-way, try:
$ ex -s +'%!grep foo' -cxa myfile.txt
Alternatively use sed or gawk.
Most installations of sed can do in-place editing, check the man page, you probably want the -i flag.
Store in a variable and then assign it to the original file:
A=$(cat aux.log | grep 'Something') && echo "${A}" > aux.log
Take a look at my slides "Field Guide To the Perl Command-Line Options" at http://petdance.com/perl/command-line-options.pdf for more ideas on what you can do in place with Perl.
cat myfile.txt | grep 'sometext' > myfile.txt
This will find sometext in myfile.txt and save it back to myfile.txt, this will accomplish what you want. Not sure about regex, but it does work for text.
Related
I'm trying to figure out a command to parse the following file content:
Operation=GET
Type=HOME
Counters=CacheHit=0,Exception=1,Validated=0
I need to extract Exception=1 into its own line. I'm fiddling with awk, sed and grep but not making much progress. Does anyone have any tips on using any unix command to perform this?
Thanks
Since your file is close to bash syntax, there is a fun little trick you can do to make bash itself parse the file. First, use some program like tr to transform the input into a something bash can parse, and then "source" that, which will create shell variables you can expand later to get the values.
source <(tr , $'\n' < file_name_goes_here)
echo $Exception
Many ways to do this. Here is one assuming the file is called "file.txt". Grab the line you want, replace everything from the start of the line up to Except with just Except, then pull out the first field using comma as the delimiter.
$ grep Exception file.txt | sed 's/.*Except/Except/g' | cut -d, -f 1
Exception=1
If you wanted to use gawk:
$ grep Exception file.txt | sed 's/.*Except/Except/g' | gawk -F, '{print $1}'
Exception=1
or just using grep and sed:
$ grep Exception file.txt | sed 's/.*\(Exception=[0-9]*\).*/\1/g'
Exception=1
or as #sheltter reminded me:
$ egrep -o "Exception=[0-9]+" file.txt
Exception=1
No need to use a mix of commands.
awk -F, 'NR==2 {print RS$1}' RS="Exception" file
Exception=1
Here we split the line by the keyword we look for RS="Exception"
If the line has two record (only when keyword is found), then
print first field, separated using command, with Record selector.
PS This only works if you have one Exception field
I have a bunch of files in a unix directory that look like the following:
filename_1234567.txt
I need to rename them by copying the last three characters of each filename
to the front of the filename like this:
567_filename_1234567.txt
Note: Both the filename and extension are variable.
I'm running this on a Solaris box.
Thanks in advance!
One possibility:
\ls *.txt | sed 's/\(.*\)\(...\).txt/mv \1\2.txt \2_\1.txt/' | sh
(probably wise to write that with echo mv, while you're double-checking it does what you think it does).
I can't decide if the alternative
sed 's/\(\(.*\)\(...\).txt\)/mv \1 \3_\2.txt/'
is more robust, or just way too fussy.
#for file in *_*.*
for file in `ls *_*.txt`
do
last_3="$(echo $file | grep -o "...\...."|cut -d'.' -f1)"
cp $file ${last_3}_${file}
done
I have a group of very large (a couple of GB's each) text files. I need to add two lines at the beginning of each of these files.
I tried using sed with the following command
sed -i '1iFirstLine'
sed -i '2iSecondLine'
The problem with sed is that it loops through the entire file, even if had to add only two lines at the beginning and therefore it takes lot of time.
Is there an alternate way to do this more efficiently, without reading the entire file?
You should try
echo "1iFirstLine" > newfile.txt
echo "2iSecondLine" >> newfile.txt
cat oldfile.txt >> newfile.txt
mv newfile.txt oldfile.txt
This one is perfectly working and its extremely fast too.
perl -pi -e '$.=0 if eof;print "first line\nsecond line\n" if ($.==1)' *.txt
Adding at the beginning is not possible without file rewrite (contrary to appending to the end). You simply cannot "shift" file content as no filesystem supports that. So you should do:
echo -e "line 1\nLine2" > tmp.txt
cat tmp2.txt oldbigfile.txt > newbigfile.txt
rm oldbigfile.txt
mv newbigfile.txt oldbigfile.txt
Note you need enough diskspace to hold both files for a while.
For grep there's a fixed string option, -F (fgrep) to turn off regex interpretation of the search string.
Is there a similar facility for sed? I couldn't find anything in the man. A recommendation of another gnu/linux tool would also be fine.
I'm using sed for the find and replace functionality: sed -i "s/abc/def/g"
Do you have to use sed? If you're writing a bash script, you can do
#!/bin/bash
pattern='abc'
replace='def'
file=/path/to/file
tmpfile="${TMPDIR:-/tmp}/$( basename "$file" ).$$"
while read -r line
do
echo "${line//$pattern/$replace}"
done < "$file" > "$tmpfile" && mv "$tmpfile" "$file"
With an older Bourne shell (such as ksh88 or POSIX sh), you may not have that cool ${var/pattern/replace} structure, but you do have ${var#pattern} and ${var%pattern}, which can be used to split the string up and then reassemble it. If you need to do that, you're in for a lot more code - but it's really not too bad.
If you're not in a shell script already, you could pretty easily make the pattern, replace, and filename parameters and just call this. :)
PS: The ${TMPDIR:-/tmp} structure uses $TMPDIR if that's set in your environment, or uses /tmp if the variable isn't set. I like to stick the PID of the current process on the end of the filename in the hopes that it'll be slightly more unique. You should probably use mktemp or similar in the "real world", but this is ok for a quick example, and the mktemp binary isn't always available.
Option 1) Escape regexp characters. E.g. sed 's/\$0\.0/0/g' will replace all occurrences of $0.0 with 0.
Option 2) Use perl -p -e in conjunction with quotemeta. E.g. perl -p -e 's/\\./,/gi' will replace all occurrences of . with ,.
You can use option 2 in scripts like this:
SEARCH="C++"
REPLACE="C#"
cat $FILELIST | perl -p -e "s/\\Q$SEARCH\\E/$REPLACE/g" > $NEWLIST
If you're not opposed to Ruby or long lines, you could use this:
alias replace='ruby -e "File.write(ARGV[0], File.read(ARGV[0]).gsub(ARGV[1]) { ARGV[2] })"'
replace test3.txt abc def
This loads the whole file into memory, performs the replacements and saves it back to disk. Should probably not be used for massive files.
If you don't want to escape your string, you can reach your goal in 2 steps:
fgrep the line (getting the line number) you want to replace, and
afterwards use sed for replacing this line.
E.g.
#/bin/sh
PATTERN='foo*[)*abc' # we need it literal
LINENUMBER="$( fgrep -n "$PATTERN" "$FILE" | cut -d':' -f1 )"
NEWSTRING='my new string'
sed -i "${LINENUMBER}s/.*/$NEWSTRING/" "$FILE"
You can do this in two lines of bash code if you're OK with reading the whole file into memory. This is quite flexible -- the pattern and replacement can contain newlines to match across lines if needed. It also preserves any trailing newline or lack thereof, which a simple loop with read does not.
mapfile -d '' < file
printf '%s' "${MAPFILE//"$pat"/"$rep"}" > file
For completeness, if the file can contain null bytes (\0), we need to extend the above, and it becomes
mapfile -d '' < <(cat file; printf '\0')
last=${MAPFILE[-1]}; unset "MAPFILE[-1]"
printf '%s\0' "${MAPFILE[#]//"$pat"/"$rep"}" > file
printf '%s' "${last//"$pat"/"$rep"}" >> file
perl -i.orig -pse 'while (($i = index($_,$s)) >= 0) { substr($_,$i,length($s), $r)}'--\
-s='$_REQUEST['\'old\'']' -r='$_REQUEST['\'new\'']' sample.txt
-i.orig in-place modification with backup.
-p print lines from the input file by default
-s enable rudimentary parsing of command line arguments
-e run this script
index($_,$s) search for the $s string
substr($_,$i,length($s), $r) replace the string
while (($i = index($_,$s)) >= 0) repeat until
-- end of perl parameters
-s='$_REQUEST['\'old\'']', -r='$_REQUEST['\'new\'']' - set $s,$r
You still need to "escape" ' chars but the rest should be straight forward.
Note: this started as an answer to How to pass special character string to sed hence the $_REQUEST['old'] strings, however this question is a bit more appropriately formulated.
You should be using replace instead of sed.
From the man page:
The replace utility program changes strings in place in files or on the
standard input.
Invoke replace in one of the following ways:
shell> replace from to [from to] ... -- file_name [file_name] ...
shell> replace from to [from to] ... < file_name
from represents a string to look for and to represents its replacement.
There can be one or more pairs of strings.
I need to rename files names like this
transform.php?dappName=Test&transformer=YAML&v_id=XXXXX
to just this
XXXXX.txt
How can I do it?
I understand that i need more than one mv command because they are at least 25000 files.
Easiest solution is to use "mmv"
You can write:
mmv "long_name*.txt" "short_#1.txt"
Where the "#1" is replaced by whatever is matched by the first wildcard.
Similarly #2 is replaced by the second, etc.
So you do something like
mmv "index*_type*.txt" "t#2_i#1.txt"
To rename index1_type9.txt to t9_i1.txt
mmv is not standard in many Linux distributions but is easily found on the net.
If you are using zsh you can also do this:
autoload zmv
zmv 'transform.php?dappName=Test&transformer=YAML&v_id=(*)' '$1.txt'
You write a fairly simple shell script in which the trickiest part is munging the name.
The outline of the script is easy (bash syntax here):
for i in 'transform.php?dappName=Test&transformer=YAML&v_id='*
do
mv $i <modified name>
done
Modifying the name has many options. I think the easiest is probably an awk one-liner like
`echo $i | awk -F'=' '{print $4}'`
so...
for i in 'transform.php?dappName=Test&transformer=YAML&v_id='*
do
mv $i `echo $i | awk -F'=' '{print $4}'`.txt
done
update
Okay, as pointed out below, this won't necessarily work for a large enough list of files; the * will overrun the command line length limit. So, then you use:
$ find . -name 'transform.php?dappName=Test&transformer=YAML&v_id=*' -prune -print |
while read
do
mv $reply `echo $reply | awk -F'=' '{print $4}'`.txt
done
Try the rename command
Or you could pipe the results of an ls into a perl regex.
You may use whatever you want to transform the name (perl, sed, awk, etc.). I'll use a python one-liner:
for file in 'transform.php?dappName=Test&transformer=YAML&v_id='*; do
mv $file `echo $file | python -c "print raw_input().split('=')[-1]"`.txt;
done
Here's the same script entirely in Python:
import glob, os
PATTERN="transform.php?dappName=Test&transformer=YAML&v_id=*"
for filename in glob.iglob(PATTERN):
newname = filename.split('=')[-1] + ".txt"
print filename, '==>', newname
os.rename(filename, newname)
Side note: you would have had an easier life saving the pages with the right name while grabbing them...
find -name '*v_id=*' | perl -lne'rename($_, qq($1.txt)) if /v_id=(\S+)/'
vimv lets you rename multiple files using Vim's text editing capabilities.
Entering vimv opens a Vim window which lists down all files and you can do pattern matching, visual select, etc to edit the names. After you exit Vim, the files will be renamed.
[Disclaimer: I'm the author of the tool]
I'd use ren-regexp, which is a Perl script that lets you mass-rename files very easily.
21:25:11 $ ls
transform.php?dappName=Test&transformer=YAML&v_id=12345
21:25:12 $ ren-regexp 's/transform.php.*v_id=(\d+)/$1.txt/' transform.php*
transform.php?dappName=Test&transformer=YAML&v_id=12345
1 12345.txt
21:26:33 $ ls
12345.txt
This should also work:
prfx='transform.php?dappName=Test&transformer=YAML&v_id='
ls $prfx* | sed s/$prfx// | xargs -Ipsx mv "$prfx"psx psx
this renamer command would do it:
$ renamer --regex --find 'transform.php?dappName=Test&transformer=YAML&v_id=(\w+)' --replace '$1.txt' *
Ok, you need to be able to run a windows binary for this.
But if you can run Total Commander, do this:
Select all files with *, and hit ctrl-M
In the Search field, paste "transform.php?dappName=Test&transformer=YAML&v_id="
(Leave Replace empty)
Press Start
It doesn't get much simpler than that.
You can also rename using regular expressions via this dialog, and you see a realtime preview of how your files are going to be renamed.