In bash, how can I print the first n elements of a list?
For example, the first 10 files in this list:
FILES=$(ls)
UPDATE: I forgot to say that I want to print the elements on one line, just like when you print the whole list with echo $FILES.
FILES=(*)
echo "${FILES[#]:0:10}"
Should work correctly even if there are spaces in filenames.
FILES=$(ls) creates a string variable. FILES=(*) creates an array. See this page for more examples on using arrays in bash. (thanks lhunath)
Why not just this to print the first 50 files:
ls -1 | head -50
FILE="$(ls | head -1)"
Handled spaces in filenames correctly too when I tried it.
My way would be:
ls | head -10 | tr "\n" " "
This will print the first 10 lines returned by ls, and then tr replaces all line breaks with spaces. Output will be on a single line.
echo $FILES | awk '{for (i = 1; i <= 10; i++) {print $i}}'
Edit: AAh, missed your comment that you needed them on one line...
echo $FILES | awk '{for (i = 1; i <= 10; i++) {printf "%s ", $i}}'
That one does that.
to do it interactively:
set $FILES && eval eval echo \\\${1..10}
to run it as a script, create foo.sh with contents
N=$1; shift; eval eval echo \\\${1..$N}
and run it as
bash foo.sh 10 $FILES
An addition to the answer of "Ayman Hourieh" and "Shawn Chin", in case it is needed for something else than content of a directory.
In newer version of bash you can use mapfile to store the directory in an array. See help mapfile
mapfile -t files_in_dir < <( ls )
If you want it completely in bash use printf "%s\n" * instead of ls, or just replace ls with any other command you need.
Now you can access the array as usual and get the data you need.
First element:
${files_in_dir[0]}
Last element (do not forget space after ":" ):
${files_in_dir[#]: -1}
Range e.g. from 10 to 20:
${files_in_dir[#]:10:20}
Attention for large directories, this is way more memory consuming than the other solutions.
FILES=$(ls)
echo $FILES | fmt -1 | head -10
Related
I have a directory with files, some have the same ID, which is given in the first part of the file name before the first underscore (always). e.g.:
S100_R1.txt
S100_R2.txt
S111_1_R1.txt
S111_R1.txt
S111_R2.txt
S333_R1.txt
I want to concatenate those identical IDs (and if possible placing the original files in another dir, e.g. output:
original files (folder)
S100_merged.txt
S111_merged.txt
S333_R1.txt
Small note: I imaging that perhaps a solution would be to place all files which will be processed by the code in a new directory and than in a second step move the files with the appended "merged" back to the original dir or something like this...
I am extremely new to bash scripting, so I really can't produce this code. I am use to R language and I can think how it should be but can't write it.
My pitiful attempt is something like this:
while IFS= read -r -d '' id; do
cat *"$id" > "./${id%.txt}_grouped.txt"
done < <(printf '%s\0' *.txt | cut -zd_ -f1- | sort -uz)
or this:
for ((k=100;k<400;k=k+1));
do
IDList= echo "S${k}_S*.txt" | awk -F'[_.]' '{$1}'
while [ IDList${k} == IDList${k+n} ]; do
cat IDList${k}_S*.txt IDList${k+n}_S*.txt S${k}_S*.txt S${k}_S*.txt >cat/S${k}_merged.txt &;
done
Sometimes there are only one version of the file (e.g. S333_R1.txt) sometime two (S100*), three (S111*) or more of the same.
I am prepared for harsh critique for this question because I am so far from a solution, but if someone would be willing to help me out I would greatly appreciate it!
while read $fil;
do
if [[ "$(find . -maxdepth 1 -name $line"_*.txt" | wc -l)" -gt "1" ]]
then
cat $line_*.txt >> "$line_merged.txt"
fi
done <<< "$(for i in *_*.txt;do echo $i;done | awk -F_ '{ print $1 }')"
Search for files with _.txt and run the output into awk, printing the strings before "_". Run this through a while loop. Check if the number of files for each prefix pattern is greater than 1 using find and if it is, cat the files with that prefix pattern into a merged file.
for id in $(ls | grep -Po '^[^_]+' | uniq) ; do
if [ $(ls ${id}_*.txt 2> /dev/null | wc -l) -gt 1 ] ; then
cat ${id}_*.txt > _${id}_merged.txt
mv ${id}_*.txt folder
fi
done
for f in _*_merged.txt ; do
mv ${f} ${f:1}
done
A plain bash loop with preprocessing:
# first get the list of files
find . -type f |
# then extract the prefix
sed 's#./\([^_]*\)_#\1\t&#' |
# then in a loop merge the files
while IFS=$'\t' read prefix file; do
cat "$file" >> "${prefix}_merged.txt"
done
That script is iterative - one file at a time. To detect if there is one file of specific prefix, we have to look at all files at a time. So first an awk script to join list of filenames with common prefix:
find . -type f | # maybe `sort |` ?
# join filenames with common prefix
awk '{
f=$0; # remember the file path
gsub(/.*\//,"");gsub(/_.*/,""); # extract prefix from filepath and store it in $0
a[$0]=a[$0]" "f # Join path with leading space in associative array indexed with prefix
}
# Output prefix and filanames separated by spaces.
# TBH a tab would be a better separator..
END{for (i in a) print i a[i]}
' |
# Read input separated by spaces into a bash array
while IFS=' ' read -ra files; do
#first array element is the prefix
prefix=${files[0]}
unset files[0]
# rest is the files
case "${#files[#]}" in
0) echo super error; ;;
# one file - preserve the filename
1) cat "${files[#]}" > "$outdir"/"${files[1]}"; ;;
# more files - do a _merged.txt suffix
*) cat "${files[#]}" > "$outdir"/"${prefix}_merged.txt"; ;;
esac
done
Tested on repl.
IDList= echo "S${k}_S*.txt"
Executes the command echo with the environment variable IDList exported and set to empty with one argument equal to S<insert value of k here>_S*.txt.
Filename expansion (ie. * -> list of files) is not executed inside " double quotes.
To assign a result of execution into a variable, use command substitution var=$( something seomthing | seomthing )
IDList${k+n}_S*.txt
The ${var+pattern} is a variable expansion that does not add two variables together. It uses pattern when var is set and does nothing when var is unset. See shell parameter expansion and this my answer on ${var-pattern}, but it's similar.
To add two numbers use arithemtic expansion $((k + n)).
awk -F'[_.]' '{$1}'
$1 is just invalid here. To print a line, print it {print %1}.
Remember to check your scripts with http://shellcheck.net
A pure bash way below. It uses only globs (no need for external commands like ls or find for this question) to enumerate filenames and an associative array (which is supported by bash since the version 4.0) in order to compute frequencies of ids. Parsing ls output to list files is questionable in bash. You may consider reading ParsingLs.
#!/bin/bash
backupdir=original_files # The directory to move the original files
declare -A count # Associative array to hold id counts
# If it is assumed that the backup directory exists prior to call, then
# drop the line below
mkdir "$backupdir" || exit
for file in [^_]*_*; do ((++count[${file%%_*}])); done
for id in "${!count[#]}"; do
if ((count[$id] > 1)); then
mv "$id"_* "$backupdir"
cat "$backupdir/$id"_* > "$id"_merged.txt
fi
done
I am looping our the a grep result. The result contains 10 lines (every line has different content). So the loop stuff in the loop gets executed 10 times.
I need to get the index, 0-9, in the run so i can do actions based on the index.
ABC=(cat test.log | grep "stuff")
counter=0
for x in $ABC
do
echo $x
((counter++))
echo "COUNTER $counter"
done
Currently the counter won't really change.
Output:
51209
120049
148480
1211441
373948
0
0
0
728304
0
COUNTER: 1
If your requirement is to only print counter(which is as per shown samples only), in that case you could use awk(if you are ok with it), this could be done in a single awk like, without creating variable and then using grep like you are doing currently, awk could perform both search and counter printing in a single shot.
awk -v counter=0 '/stuff/{print "counter=" counter++}' Input_file
Replace stuff string above with the actual string you are looking for and place your actual file name for Input_file in above.
This should print like:
counter=1
counter=2
........and so on
Your shell script contains what should be an obvious syntax error.
ABC=(cat test.log | grep "stuff")
This fails with
-bash: syntax error near unexpected token `|'
There is no need to save the output in a variable if you only want to process one at a time (and obviously no need for the useless cat).
grep "stuff" test.log | nl
gets you numbered lines, though the index will be 1-based, not zero-based.
If you absolutely need zero-based, refactoring to Awk should solve it easily:
awk '/stuff/ { print n++, $0 }' test.log
If you want to loop over this and do something more with this information,
awk '/stuff/ { print n++, $0 }' test.log |
while read -r index output; do
echo index is "$index"
echo output is "$output"
done
Because the while loop executes in a subshell the value of index will not be visible outside of the loop. (I guess that's what your real code did with the counter as well. I don't think that part of the code you posted will repro either.)
Do not store the result of grep in a scalar variable $ABC.
If the line of the log file contains whitespaces, the variable $x
is split on them due to the word splitting of bash.
(BTW the statement ABC=(cat test.log | grep "stuff") causes a syntax error.)
Please try something like:
readarray -t abc < <(grep "stuff" test.log)
for x in "${abc[#]}"
do
echo "$x"
echo "COUNTER $((++counter))"
done
or
readarray -t abc < <(grep "stuff" test.log)
for i in "${!abc[#]}"
do
echo "${abc[i]}"
echo "COUNTER $((i + 1))"
done
you can use below increment statement-
counter=$(( $counter + 1));
I have hundreds of numbered files
file_001.txt
file_002.txt
file_003.txt
...
and and the same number of letters in a separate file
letters.txt:
abc
def
ghi
...
How can I rename the files in this way:
file_001_abc.txt
file_002_def.txt
file_003_ghi.txt
Thanks in advance, very much!
A combination of paste and awk came to my mind first.
paste files.txt letters.txt | awk '{split($1,file,"."); print file[1]"_"$2"."file[2]}'
If you do not have a list of the files you could replace files.txt for example by <(ls -1) but this depends on your specific setup.
count=0
for i in `cat f1`;do
let count++
var=$(head -$count letters.txt | tail -1)
mv $i ${i%.txt}_$var.txt
done
Hope this helps
Thanks
I commented the line with xargs so you can check the script.
When you like it, remove the comment.
start=0
while read next; do
(( start = start + 1 ));
printf "mv file_%03d.txt file_%03d_%s.txt\n" ${start} ${start} ${next}
# printf "file_%03d.txt file_%03d_%s.txt" ${start} ${start} ${next} | xargs mv
done < letters.txt
I have a list of files where two subsequent ones always belong together. I would like a for loop extract two files out of this list per iteration, and then work on these two files at a time (for an example, let's say I want to just concatenate, i.e. cat the two files).
In a simple case, my list of files is this:
FILES="file1_mateA.txt file1_mateB.txt file2_mateA.txt file2_mateB.txt"
I could hack around it and say
FILES="file1 file2"
for file in $FILES
do
actual_mateA=${file}_mateA.txt
actual_mateB=${file}_mateB.txt
cat $actual_mateA $actual_mateB
done
But I would like to be able to handle lists where mate A and mate B have arbitrary names, e.g.:
FILES="first_file_first_mate.txt first_file_second_mate.txt file2_mate1.txt file2_mate2.txt"
Is there a way to extract two values out of $FILES per iteration?
Use an array for the list:
files=(fileA1 fileA2 fileB1 fileB2)
for (( i=0; i<${#files[#]} ; i+=2 )) ; do
echo "${files[i]}" "${files[i+1]}"
done
You could read the values from a while loop and use xargs to restrict each read operation to two tokens.
files="filaA1 fileA2 fileB1 fileB2"
while read -r a b; do
echo $a $b
done < <(echo $files | xargs -n2)
You could use xargs(1), e.g.
ls -1 *.txt | xargs -n2 COMMAND
The switch -n2 let xargs select 2 consecutive filenames from the pipe output which are handed down do the COMMAND
To concatenate the 10 files file01.txt ... file10.txt pairwise
one can use
ls *.txt | xargs -n2 sh -c 'cat $# > $1.$2.joined' dummy
to get the 5 result files
file01.txt.file02.txt.joined
file03.txt.file04.txt.joined
file05.txt.file06.txt.joined
file07.txt.file08.txt.joined
file09.txt.file10.txt.joined
Please see 'info xargs' for an explantion.
How about this:
park=''
for file in $files # wherever you get them from, maybe $(ls) or whatever
do
if [ "$park" = '' ]
then
park=$file
else
process "$park" "$file"
park=''
fi
done
In each odd iteration it just stores the value (in park) and in each even iteration it then uses the stored and the current value.
Seems like one of those things awk is suited for
$ awk '{for (i = 1; i <= NF; i+=2) if( i+1 <= NF ) print $i " " $(i+1) }' <<< "$FILES"
file1_mateA.txt file1_mateB.txt
file2_mateA.txt file2_mateB.txt
You could then loop over it by setting IFS=$'\n'
e.g.
#!/bin/bash
FILES="file1_mateA.txt file1_mateB.txt file2_mateA.txt file2_mateB.txt file3_mat
input=$(awk '{for (i = 1; i <= NF; i+=2) if( i+1 <= NF ) print $i " " $(i+1) }'
IFS=$'\n'
for set in $input; do
cat "$set" # or something
done
Which will try to do
$ cat file1_mateA.txt file1_mateB.txt
$ cat file2_mateA.txt file2_mateB.txt
And ignore the odd case without the match.
You can transform you string to array and read this new array by elements:
#!/bin/bash
string="first_file_first_mate.txt first_file_second_mate.txt file2_mate1.txt file2_mate2.txt"
array=(${string})
size=${#array[*]}
idx=0
while [ "$idx" -lt "$size" ]
do
echo ${array[$idx]}
echo ${array[$(($idx+1))]}
let "idx=$idx+2"
done
If you have delimiter in string different from space (i.e. ;) you can use the following transformation to array:
array=(${string//;/ })
You could try something like this:
echo file1 file2 file3 file4 | while read -d ' ' a; do read -d ' ' b; echo $a $b; done
file1 file2
file3 file4
Or this, somewhat cumbersome technique:
echo file1 file2 file3 file4 |tr " " "\n" | while :;do read a || break; read b || break; echo $a $b; done
file1 file2
file3 file4
Say if i wanted to do this command:
(cat file | wc -l)/2
and store it in a variable such as middle, how would i do it?
I know its simply not the case of
$middle=$(cat file | wc -l)/2
so how would i do it?
middle=$((`wc -l < file` / 2))
middle=$((`wc -l file | awk '{print $1}'`/2))
This relies on Bash being able to reference the first element of an array using scalar syntax and that is does word splitting on white space by default.
middle=($(wc -l file)) # create an array which looks like: middle='([0]="57" [1]="file")'
middle=$((middle / 2)) # do the math on ${middle[0]}
The second line can also be:
((middle /= 2))
When assigning variables, you don't use the $
Here is what I came up with:
mid=$(cat file | wc -l)
middle=$((mid/2))
echo $middle
The double parenthesis are important on the second line. I'm not sure why, but I guess it tells Bash that it's not a file?
using awk.
middle=$(awk 'END{print NR/2}' file)
you can also make your own "wc" using just the shell.
linec(){
i=0
while read -r line
do
((i++))
done < "$1"
echo $i
}
middle=$(linec "file")
echo "$middle"