I have a text file: file.txt, with several thousand lines. It contains a lot of junk lines which I am not interested in, so I use the cut command to regex for the lines I am interested in first. For each entry I am interested in, it will be listed twice in the text file: Once in a "definition" section, another in a "value" section. I want to retrieve the first value from the "definition" section, and then for each entry found there find it's corresponding "value" section entry.
The first entry starts with ' gl_ ', while the 2nd entry would look like ' "gl_ ', starting with a '"'.
This is the code I have so far for looping through the text document, which then retrieves the values I am interested in and appends them to a .csv file:
while read -r line
do
if [[ $line == gl_* ]] ; then (param=$(cut -d'\' -f 1 $line) | def=$(cut -d'\' -f 2 $line) | type=$(cut -d'\' -f 4 $line) | prompt=$(cut -d'\' -f 8 $line))
while read -r glline
do
if [[ $glline == '"'$param* ]] ; then val=$(cut -d'\' -f 3 $glline) |
"$project";"$param";"$val";"$def";"$type";"$prompt" >> /filepath/file.csv
done < file.txt
done < file.txt
This seems to throw some syntax errors related to unexpected tokens near the first 'done' statement.
Example of text that needs to be parsed, and paired:
gl_one\User Defined\1\String\1\\1\Some Text
gl_two\User Defined\1\String\1\\1\Some Text also
gl_three\User Defined\1\Time\1\\1\Datetime now
some\junk
"gl_one\1\Value1
some\junk
"gl_two\1\Value2
"gl_three\1\Value3
So effectively, the while loop reads each line until it hits the first line that starts with 'gl_', which then stores that value (ie. gl_one) as a variable 'param'.
It then starts the nested while loop that looks for the line that starts with a ' " ' in front of the gl_, and is equivalent to the 'param' value. In other words, the
script should couple the lines gl_one and "gl_one, gl_two and "gl_two, gl_three and "gl_three.
The text file is large, and these are settings that have been defined this way. I need to collect the values for each gl_ parameter, to save them together in a .csv file with their corresponding "gl_ values.
Wanted regex output stored in variables would be something like this:
first while loop:
$param = gl_one, $def = User Defined, $type = String, $prompt = Some Text
second while loop:
$val = Value1
Then it stores these variables to the file.csv, with semi-colon separators.
Currently, I have an error for the first 'done' statement, which seems to indicate an issue with the quotation marks. Apart from this,
I am looking for general ideas and comments to the script. I.e, not entirely sure I am looking for the quotation mark parameters "gl_ correctly, or if the
semi-colons as .csv separators are added correctly.
Edit: Overall, the script runs now, but extremely slow due to the inner while loop. Is there any faster way to match the two lines together and add them to the .csv file?
Any ideas and comments?
This will generate a file containing the data you want:
cat file.txt | grep gl_ | sed -E "s/\"//" | sort | sed '$!N;s/\n/\\/' | awk -F'\' '{print $1"; "$5"; "$7"; "$NF}' > /filepath/file.csv
It uses grep to extract all lines containing 'gl_'
then sed to remove the leading '"' from the lines that contain one [I have assumed there are no further '"' in the line]
The lines are sorted
sed removes the return from each pair of lines
awk then prints
the required columns according to your requirements
Output routed to the file.
LANG=C sort -t\\ -sd -k1,1 <file.txt |\
sed '
/^gl_/{ # if definition
N; # append next line to buffer
s/\n"gl_[^\\]*//; # if value, strip first column
t; # and start next loop
}
D; # otherwise, delete the line
' |\
awk -F\\ -v p="$project" -v OFS=\; '{print p,$1,$10,$2,$4,$8 }' \
>>/filepath/file.csv
sort lines so gl_... appears immediately before "gl_... (LANG fixes LC_TYPE) - assumes definition appears before value
sed to help ensure matching definition and value (may still fail if duplicate/missing value), and tidy for awk
awk to pull out relevant fields
Input file, fruits.txt:
JAN,APPLE
FEB,MANGO
JAN,ORANGE
MAR,APPLE
FEB,APPLE
Expected output file:
MAR,APPLE
FEB,APPLE
JAN,ORANGE
For getting the above output, below code is used:
#!/bin/sh
declare -A m_arr
cat fruits.txt > /tmp/ID.part
while read line
do
Month=$(echo $line | cut -d, -f1)
Fruits=$(echo $line | cut -d, -f2)
m_arr[${Month}]=${Fruits}
done < /tmp/ID.part
for i in ${!m_arr[#]}
do
echo "$i,${m_arr[$i]}"
done
This works fine for small number of data in input file. I have 200 000 entries and observed that cut command is very slow. Tried with awk as well, did not get a better result. My requirement is to read the file from row1, with the key as column1. I need to updated entry for each key.
I think this can be done pretty easily with Awk, you just need to hash the values of $1 in $2 once you delimit the file with a , separator
awk -v FS=, -v OFS=, '{key[$1]=$2; next}END{for (i in key) print i,key[i]}' file
Also if you want to speed up things while processing a million line file, you can change the localization settings to speed up the execution while parsing, you can pass LC_ALL=C locally to the command. See Stéphane Chazelas's answer on what "LC_ALL=C" does?
In bash version 4, you can declare an associative array and populate it with the result of read, splitting your lines with a custom IFS:
$ declare -A a
$ while IFS=, read key value; do a["$key"]="$value"; done < fruits.txt
$ declare -p a
declare -A a=([MAR]="APPLE" [FEB]="APPLE" [JAN]="ORANGE" )
If you want to generate that specific output from the array, you'll also require a loop:
$ for key in "${!a[#]}"; do printf '%s,%s\n' "$key" "${a[$key]}"; done
MAR,APPLE
FEB,APPLE
JAN,ORANGE
The shortest one using GNU datamash:
datamash -st, -g1 last 2 <file
g1 - group by the 1st column
last 2 - keep the last value of the group
The output:
FEB,APPLE
JAN,ORANGE
MAR,APPLE
I have a file links.txt:
1 a.sh
3 b.sh
6 c.sh
4 d.sh
So, if i pass 1,4 as parameters to another file(master.sh), a.sh and d.sh should be stored in a variable.
sed '3!d' would print the 3rd line, but not the line that starts with 3. For that, you need sed '/^3 /!d'. The problem is you can't combine them for more lines, as this means "Delete everything that doesn't start with a 3", which means all other lines will be missed. So, use sed -n '/^3 /p' instead, i.e. don't print by default and tell sed what lines to print, not what lines to delete.
You can loop over the argument and create a sed script from them that prints the lines, then run sed using this output:
#!/bin/bash
file=$1
shift
for id in "$#" ; do
echo "/^$id /p"
done | sed -nf- "$file"
Run as script.sh filename 3 4.
If you want to remove the id from the output, you can either use
cut -f2 -d' '
or you can modify the generated sed script to do the work
echo "/^$id /s/.* //p"
i.e. only print if the substitution was successful.
This loops through each argument and greps for it in the links file. The result is piped into cut where we specify the delimiter as a space with -d flag and the field number as 2 with -f flag. Finally this is appended to the array called files.
links="links.txt"
files=()
for arg in $#; do
files=("${files[#]}" `grep "^$arg" "$links" | cut -d" " -f2`)
done;
echo ${files[#]}
Usage:
$ ./master.sh 1 4
a.sh d.sh
Edit:
As pointed out by mklement0, the solution above reads the file once per arg. The following first builds the pattern then reads the file just once.
links="links.txt"
pattern="^$1\s"
for arg in ${#:2}; do
pattern+="|^$arg\s"
done
files=$(grep -E "$pattern" "$links" | cut -d" " -f2)
echo ${files[#]}
Usage:
$ ./master.sh 1 4
a.sh d.sh
Here is another example with grep and cut:
#!/bin/bash
for line in $(grep "$1\|$2" links.txt|cut -d' ' -f2)
do
echo $line
done
Example of usage:
./master.sh 1 4
a.sh
d.sh
Why not just stores the values and call them at will:
items=()
while read -r num file
do
items[num]="$file"
done<links.txt
for arg
do
echo "${items[arg]}"
done
Now you can use the items array any time you like :)
The following awk solution:
preserves the argument order; that is, the results reflect the order in which the lookup values were specified (as opposed to the order in which the lookup values happen to occur in the file).
If that is not important (i.e., if outputting the results in file order is acceptable), the readarray technique below can be combined with this one-liner, which is a generalized variant of Panta's answer:
grep -f <(printf "^%s\n" "$#") links.txt | cut -d' ' -f2-
performs well, because the input file is only read once; the only requirement is that all key-value pairs fit into memory as a whole (as a single associative Awk array (dictionary)).
works with any lookup values that don't have embedded whitespace.
Similarly, the assumption is that the output column values (containing values such as a.sh in the sample input) have no embedded whitespace. awk doesn't handle quoted fields well, so more work would be needed.
#!/bin/bash
readarray -t files < <(
awk -v idList="$*" '
BEGIN { count=split(idList, idArr); for (i in idArr) idDict[idArr[i]]++ }
$1 in idDict { idDict[$1] = $2 }
END { for (i=1; i<=count; ++i) print idDict[idArr[i]] }
' links.txt
)
# Print results.
printf '%s\n' "${files[#]}"
readarray -t files reads stdin input (<) line by line into array variable files.
Note: readarray requires Bash v4+; on Bash 3.x, such as on macOS, replace this part with
IFS=$'\n' read -d '' -ra files
<(...) is a Bash process substitution that, loosely speaking, presents the output from the enclosed command as if it were (self-deleting) temporary file.
This technique allows readarray to run in the current shell (as opposed to a subshell if a pipeline had been used), which is necessary for the files variable to remain defined in the remainder of the script.
The awk command breaks down as follows:
-v idList="$*" passes the space-separated list of all command-line arguments as a single string to Awk variable idList.
Note that this assumes that the arguments have no embedded spaces, which is indeed the case here and also generally the case with identifiers.
BEGIN { ... } is only executed once, before the individual lines are processed:
split(idList, idArr) splits the input ID list into an array by whitespace and stores the result in idArr.
for (i in idArr) idDict[idArr[i]]++ } then converts the (conceptually regular) array into associative array idDict (dictionary), whose keys are the input IDs - this enables efficient lookup by ID later, and also allows storing the lookup result for each ID.
$1 in idDict { idDict[$1] = $2 } is processed for every input line:
Pattern $1 in idDict returns true if the line's first whitespace-separated field ($1) - e.g., 6 - is among the keys (in) of associative array idDict, and, if so, executes the associated action ({...}).
Action { idDict[$1] = $2 } then assigns the second field ($2) - e.g., c.sh - to the iDict entry for key $1.
END { ... } is executed once, after all input lines have been processed:
for (i=1; i<=count; ++i) print idDict[idArr[i]] loops over all input IDs in order and prints each ID's lookup result, which is the value of the dictionary entry with that ID.
I have the following script where I'm parsing 2 csv files to find a MATCH the files have 10000 lines each one. But the processing is taking a long time!!! Is this normal?
My script:
#!/bin/bash
IFS=$'\n'
CSV_FILE1=$1;
CSV_FILE2=$2;
sort -t';' $CSV_FILE1 >> Sorted_CSV1
sort -t';' $CSV_FILE2 >> Sorted_CSV2
echo "PATH1 ; NAME1 ; SIZE1 ; CKSUM1 ; PATH2 ; NAME2 ; SIZE2 ; CKSUM2" >> 'mapping.csv'
while read lineCSV1 #Parse 1st CSV file
do
PATH1=`echo $lineCSV1 | awk '{print $1}'`
NAME1=`echo $lineCSV1 | awk '{print $3}'`
SIZE1=`echo $lineCSV1 | awk '{print $7}'`
CKSUM1=`echo $lineCSV1 | awk '{print $9}'`
while read lineCSV2 #Parse 2nd CSV file
do
PATH2=`echo $lineCSV2 | awk '{print $1}'`
NAME2=`echo $lineCSV2 | awk '{print $3}'`
SIZE2=`echo $lineCSV2 | awk '{print $7}'`
CKSUM2=`echo $lineCSV2 | awk '{print $9}'`
# Test if NAM1 MATCHS NAME2
if [[ $NAME1 == $NAME2 ]]; then
#Test checksum OF THE MATCHING NAME
if [[ $CKSUM1 != $CKSUM2 ]]; then
#MAPPING OF THE MATCHING LINES
echo $PATH1 ';' $NAME1 ';' $SIZE1 ';' $CKSUM1 ';' $PATH2 ';' $NAME2 ';' $SIZE2 ';' $CKSUM2 >> 'mapping.csv'
fi
break #When its a match break the while loop and go the the next Row of the 1st CSV File
fi
done < Sorted_CSV2 #Done CSV2
done < Sorted_CSV1 #Done CSV1
This is a quadratic order. Also, see Tom Fenech comment: You are calling awk several times inside a loop inside another loop. Instead of using awk for the fields in every line try setting the IFS shell variable to ";" and read the fields directly in read commands:
IFS=";"
while read FIELD11 FIELD12 FIELD13; do
while read FIELD21 FIELD22 FIELD23; do
...
done <Sorted_CSV2
done <Sorted_CSV1
Though, this would be still O(N^2) and very inefficient. It seems you are matching 2 fields by a coincident field. This task is easier and faster to accomplish by using join command line utility, and would reduce order from O(N^2) to O(N).
Whenever you say "Does this file/data list/table have something that matches this file/data list/table?", you should think of associative arrays (sometimes called hashes).
An associative array is keyed by a particular value and each key is associated with a value. The nice thing is that finding a key is extremely fast.
In your loop of a loop, you have 10,000 lines in each file. You're outer loop executed 10,000 times. Your inner loop may execute 10,000 times for each and every line in your first file. That's 10,000 x 10,000 times you go through that inner loop. That's potentially looping 100 million times through that inner loop. Think you can see why your program might be a little slow?
In this day and age, having a 10,000 member associative array isn't that bad. (Imagine doing this back in 1980 on a MS-DOS system with 256K. It just wouldn't work). So, let's go through the first file, create a 10,000 member associative array, and then go through the second file looking for matching lines.
Bash 4.x has associative arrays, but I only have Bash 3.2 on my system, so I can't really give you an answer in Bash.
Besides, sometimes Bash isn't the answer to a particular issue. Bash can be a bit slow and the syntax can be error prone. Awk might be faster, but many versions don't have associative arrays. This is really a job for a higher level scripting language like Python or Perl.
Since I can't do a Bash answer, here's a Perl answer. Maybe this will help. Or, maybe this will inspire someone who has Bash 4.x can give an answer in Bash.
I Basically open the first file and create an associative array keyed by the checksum. If this is a sha1 checksum, it should be unique for all files (unless they're an exact match). If you don't have a sha1 checksum, you'll need to massage the structure a wee bit, but it's pretty much the same idea.
Once I have the associative array figured out, I then open file #2 and simply see if the checksum already exists in the file. If it does, I know I have a matching line, and print out the two matches.
I have to loop 10,000 times in the first file, and 10,000 times in the second. That's only 20,000 loops instead of 10 million that's 20,000 times less looping which means the program will run 20,000 times faster. So, if it takes 2 full days for your program to run with a double loop, an associative array solution will work in less than one second.
#! /usr/bin/env perl
#
use strict;
use warnings;
use autodie;
use feature qw(say);
use constant {
FILE1 => "file1.txt",
FILE2 => "file2.txt",
MATCHING => "csv_matches.txt",
};
#
# Open the first file and create the associative array
#
my %file_data;
open my $fh1, "<", FILE1;
while ( my $line = <$fh1> ) {
chomp $line;
my ( $path, $blah, $name, $bather, $yadda, $tl_dr, $size, $etc, $check_sum ) = split /\s+/, $line;
#
# The main key is "check_sum" which **should** be unique, especially if it's a sha1
#
$file_data{$check_sum}->{PATH} = $path;
$file_data{$check_sum}->{NAME} = $name;
$file_data{$check_sum}->{SIZE} = $size;
}
close $fh1;
#
# Now, we have the associative array keyed by the data we want to match, read file 2
#
open my $fh2, "<", FILE2;
open my $csv_fh, ">", MATCHING;
while ( my $line = <$fh2> ) {
chomp $line;
my ( $path, $blah, $name, $bather, $yadda, $tl_dr, $size, $etc, $check_sum ) = split /\s+/, $line;
#
# If there is a matching checksum in file1, we know we have a matching entry
#
if ( exists $file_data{$check_sum} ) {
printf {$csv_fh} "%s;%s:%s:%s:%s:%s\n",
$file_data{$check_sum}->{PATH}, $file_data{$check_sum}->{NAME}, $file_data{$check_sum}->{SIZE},
$path, $name, $size;
}
}
close $fh2;
close $csv_fh;
BUGS
(A good manpage always list issues!)
This assumes one match per file. If you have multiple duplicates in file1 or file2, you will only pick up the last one.
This assumes a sha256 or equivalent checksum. In such a checksum, it is extremely unlikely that two files will have the same checksum unless they match. A 16bit checksum from the historic sum command may have collisions.
Although a proper database engine would make a much better tool for this, it is still very well possible to do it with awk.
The trick is to sort your data, so that records with the same name are grouped together. Then a single pass from top to bottom is enough to find the matches. This can be done in linear time.
In detail:
Insert two columns in both CSV files
Make sure every line starts with the name. Also add a number (either 1 or 2) which denotes from which file the line originates. We will need this when we merge the two files together.
awk -F';' '{ print $2 ";1;" $0 }' csvfile1 > tmpfile1
awk -F';' '{ print $2 ";2;" $0 }' csvfile2 > tmpfile2
Concatenate the files, then sort the lines
sort tmpfile1 tmpfile2 > tmpfile3
Scan the result, report the mismatches
awk -F';' -f scan.awk tmpfile3
Where scan.awk contains:
BEGIN {
origin = 3;
}
$1 == name && $2 > origin && $6 != checksum {
print record;
}
{
name = $1;
origin = $2;
checksum = $6;
sub(/^[^;]*;.;/, "");
record = $0;
}
Putting it all together
Crammed together into a Bash oneliner, without explicit temporary files:
(awk -F';' '{print $2";1;"$0}' csvfile1 ; awk -F';' '{print $2";2;"$0}' csvfile2) | sort | awk -F';' 'BEGIN{origin=3}$1==name&&$2>origin&&$6!=checksum{print record}{name=$1;origin=$2;checksum=$6;sub(/^[^;]*;.;/,"");record=$0;}'
Notes:
If the same name appears more than once in csvfile1, then all but the last one are ignored.
If the same name appears more than once in csvfile2, then all but the first one are ignored.
If I have a csv file, is there a quick bash way to print out the contents of only any single column? It is safe to assume that each row has the same number of columns, but each column's content would have different length.
You could use awk for this. Change '$2' to the nth column you want.
awk -F "\"*,\"*" '{print $2}' textfile.csv
yes. cat mycsv.csv | cut -d ',' -f3 will print 3rd column.
The simplest way I was able to get this done was to just use csvtool. I had other use cases as well to use csvtool and it can handle the quotes or delimiters appropriately if they appear within the column data itself.
csvtool format '%(2)\n' input.csv
Replacing 2 with the column number will effectively extract the column data you are looking for.
Landed here looking to extract from a tab separated file. Thought I would add.
cat textfile.tsv | cut -f2 -s
Where -f2 extracts the 2, non-zero indexed column, or the second column.
Here is a csv file example with 2 columns
myTooth.csv
Date,Tooth
2017-01-25,wisdom
2017-02-19,canine
2017-02-24,canine
2017-02-28,wisdom
To get the first column, use:
cut -d, -f1 myTooth.csv
f stands for Field and d stands for delimiter
Running the above command will produce the following output.
Output
Date
2017-01-25
2017-02-19
2017-02-24
2017-02-28
To get the 2nd column only:
cut -d, -f2 myTooth.csv
And here is the output
Output
Tooth
wisdom
canine
canine
wisdom
incisor
Another use case:
Your csv input file contains 10 columns and you want columns 2 through 5 and columns 8, using comma as the separator".
cut uses -f (meaning "fields") to specify columns and -d (meaning "delimiter") to specify the separator. You need to specify the latter because some files may use spaces, tabs, or colons to separate columns.
cut -f 2-5,8 -d , myvalues.csv
cut is a command utility and here is some more examples:
SYNOPSIS
cut -b list [-n] [file ...]
cut -c list [file ...]
cut -f list [-d delim] [-s] [file ...]
I think the easiest is using csvkit:
Gets the 2nd column:
csvcut -c 2 file.csv
However, there's also csvtool, and probably a number of other csv bash tools out there:
sudo apt-get install csvtool (for Debian-based systems)
This would return a column with the first row having 'ID' in it.
csvtool namedcol ID csv_file.csv
This would return the fourth row:
csvtool col 4 csv_file.csv
If you want to drop the header row:
csvtool col 4 csv_file.csv | sed '1d'
First we'll create a basic CSV
[dumb#one pts]$ cat > file
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
Then we get the 1st column
[dumb#one pts]$ awk -F , '{print $1}' file
a
1
a
1
Many answers for this questions are great and some have even looked into the corner cases.
I would like to add a simple answer that can be of daily use... where you mostly get into those corner cases (like having escaped commas or commas in quotes etc.,).
FS (Field Separator) is the variable whose value is dafaulted to
space. So awk by default splits at space for any line.
So using BEGIN (Execute before taking input) we can set this field to anything we want...
awk 'BEGIN {FS = ","}; {print $3}'
The above code will print the 3rd column in a csv file.
The other answers work well, but since you asked for a solution using just the bash shell, you can do this:
AirBoxOmega:~ d$ cat > file #First we'll create a basic CSV
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
a,b,c,d,e,f,g,h,i,k
1,2,3,4,5,6,7,8,9,10
And then you can pull out columns (the first in this example) like so:
AirBoxOmega:~ d$ while IFS=, read -a csv_line;do echo "${csv_line[0]}";done < file
a
1
a
1
a
1
a
1
a
1
a
1
So there's a couple of things going on here:
while IFS=, - this is saying to use a comma as the IFS (Internal Field Separator), which is what the shell uses to know what separates fields (blocks of text). So saying IFS=, is like saying "a,b" is the same as "a b" would be if the IFS=" " (which is what it is by default.)
read -a csv_line; - this is saying read in each line, one at a time and create an array where each element is called "csv_line" and send that to the "do" section of our while loop
do echo "${csv_line[0]}";done < file - now we're in the "do" phase, and we're saying echo the 0th element of the array "csv_line". This action is repeated on every line of the file. The < file part is just telling the while loop where to read from. NOTE: remember, in bash, arrays are 0 indexed, so the first column is the 0th element.
So there you have it, pulling out a column from a CSV in the shell. The other solutions are probably more practical, but this one is pure bash.
You could use GNU Awk, see this article of the user guide.
As an improvement to the solution presented in the article (in June 2015), the following gawk command allows double quotes inside double quoted fields; a double quote is marked by two consecutive double quotes ("") there. Furthermore, this allows empty fields, but even this can not handle multiline fields. The following example prints the 3rd column (via c=3) of textfile.csv:
#!/bin/bash
gawk -- '
BEGIN{
FPAT="([^,\"]*)|(\"((\"\")*[^\"]*)*\")"
}
{
if (substr($c, 1, 1) == "\"") {
$c = substr($c, 2, length($c) - 2) # Get the text within the two quotes
gsub("\"\"", "\"", $c) # Normalize double quotes
}
print $c
}
' c=3 < <(dos2unix <textfile.csv)
Note the use of dos2unix to convert possible DOS style line breaks (CRLF i.e. "\r\n") and UTF-16 encoding (with byte order mark) to "\n" and UTF-8 (without byte order mark), respectively. Standard CSV files use CRLF as line break, see Wikipedia.
If the input may contain multiline fields, you can use the following script. Note the use of special string for separating records in output (since the default separator newline could occur within a record). Again, the following example prints the 3rd column (via c=3) of textfile.csv:
#!/bin/bash
gawk -- '
BEGIN{
RS="\0" # Read the whole input file as one record;
# assume there is no null character in input.
FS="" # Suppose this setting eases internal splitting work.
ORS="\n####\n" # Use a special output separator to show borders of a record.
}
{
nof=patsplit($0, a, /([^,"\n]*)|("(("")*[^"]*)*")/, seps)
field=0;
for (i=1; i<=nof; i++){
field++
if (field==c) {
if (substr(a[i], 1, 1) == "\"") {
a[i] = substr(a[i], 2, length(a[i]) - 2) # Get the text within
# the two quotes.
gsub(/""/, "\"", a[i]) # Normalize double quotes.
}
print a[i]
}
if (seps[i]!=",") field=0
}
}
' c=3 < <(dos2unix <textfile.csv)
There is another approach to the problem. csvquote can output contents of a CSV file modified so that special characters within field are transformed so that usual Unix text processing tools can be used to select certain column. For example the following code outputs the third column:
csvquote textfile.csv | cut -d ',' -f 3 | csvquote -u
csvquote can be used to process arbitrary large files.
I needed proper CSV parsing, not cut / awk and prayer. I'm trying this on a mac without csvtool, but macs do come with ruby, so you can do:
echo "require 'csv'; CSV.read('new.csv').each {|data| puts data[34]}" | ruby
I wonder why none of the answers so far have mentioned csvkit.
csvkit is a suite of command-line tools for converting to and working
with CSV
csvkit documentation
I use it exclusively for csv data management and so far I have not found a problem that I could not solve using cvskit.
To extract one or more columns from a cvs file you can use the csvcut utility that is part of the toolbox. To extract the second column use this command:
csvcut -c 2 filename_in.csv > filename_out.csv
csvcut reference page
If the strings in the csv are quoted, add the quote character with the q option:
csvcut -q '"' -c 2 filename_in.csv > filename_out.csv
Install with pip install csvkit or sudo apt install csvkit.
Simple solution using awk. Instead of "colNum" put the number of column you need to print.
cat fileName.csv | awk -F ";" '{ print $colNum }'
csvtool col 2 file.csv
where 2 is the column you are interested in
you can also do
csvtool col 1,2 file.csv
to do multiple columns
You can't do it without a full CSV parser.
If you know your data will not be quoted, then any solution that splits on , will work well (I tend to reach for cut -d, -f1 | sed 1d), as will any of the CSV manipulation tools.
If you want to produce another CSV file, then xsv, csvkit, csvtool, or other CSV manipulation tools are appropriate.
If you want to extract the contents of one single column of a CSV file, unquoting them so that they can be processed by subsequent commands, this Python 1-liner does the trick for CSV files with headers:
python -c 'import csv,sys'$'\n''for row in csv.DictReader(sys.stdin): print(row["message"])'
The "message" inside of the print function selects the column.
If the CSV file doesn't have headers:
python -c 'import csv,sys'$'\n''for row in csv.reader(sys.stdin): print(row[1])'
Python's CSV library supports all kinds of CSV dialects, so if your CSV file uses different conventions, it's possible to support them with relatively little change to the code.
Been using this code for a while, it is not "quick" unless you count "cutting and pasting from stackoverflow".
It uses ${##} and ${%%} operators in a loop instead of IFS. It calls 'err' and 'die', and supports only comma, dash, and pipe as SEP chars (that's all I needed).
err() { echo "${0##*/}: Error:" "$#" >&2; }
die() { err "$#"; exit 1; }
# Return Nth field in a csv string, fields numbered starting with 1
csv_fldN() { fldN , "$1" "$2"; }
# Return Nth field in string of fields separated
# by SEP, fields numbered starting with 1
fldN() {
local me="fldN: "
local sep="$1"
local fldnum="$2"
local vals="$3"
case "$sep" in
-|,|\|) ;;
*) die "$me: arg1 sep: unsupported separator '$sep'" ;;
esac
case "$fldnum" in
[0-9]*) [ "$fldnum" -gt 0 ] || { err "$me: arg2 fldnum=$fldnum must be number greater or equal to 0."; return 1; } ;;
*) { err "$me: arg2 fldnum=$fldnum must be number"; return 1;} ;;
esac
[ -z "$vals" ] && err "$me: missing arg2 vals: list of '$sep' separated values" && return 1
fldnum=$(($fldnum - 1))
while [ $fldnum -gt 0 ] ; do
vals="${vals#*$sep}"
fldnum=$(($fldnum - 1))
done
echo ${vals%%$sep*}
}
Example:
$ CSVLINE="example,fields with whitespace,field3"
$ $ for fno in $(seq 3); do echo field$fno: $(csv_fldN $fno "$CSVLINE"); done
field1: example
field2: fields with whitespace
field3: field3
You can also use while loop
IFS=,
while read name val; do
echo "............................"
echo Name: "$name"
done<itemlst.csv