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