In everyday data science work, we'll often encounter files so large that opening them in our spreadsheet or text editor becomes impractical.
That's where less command comes to the rescue - it's a simple yet powerful tool to efficiently handle large files right from your command line.
If you haven’t heard of it, please open your terminal and type less (Yes, ironically, it gives you more).
And if you’re already familiar with it, please stick around! There may still be some useful options you haven’t seen. I definitely had!
In this post, I'll share less options that make it easy to explore, search, and navigate through large files - whether you're working with CSVs, JSON, or even XMLs.
less is more ?The literal phrase is related to Unix history.
The original more command was an early Unix tool to view text files one screen at a time.
Later, less was introduced, as a more powerful alternative to more.
So literally, less is more because it does more than more.
This idea also roots into the Unix philosophy: "do one thing and do it well."
I believe that this principle is valuable not just in Unix, but in our life. Embracing a "less is more' mindset helps us focus on what's essential and avoid unnessary complexity.
less special ?less loads only what's needed into memory, so we can view even huge datasets instantly - much faster than commands that read the entire file into memory./pattern to search forward or ?pattern to search backward.j and k, respectively.cat data.csv | less or grep pattern data.csv | lessless1. Explore a large CSV file:
# -N: show line numbers
# -S: prevents line wrapping - useful for wide tables
$ less -N -S winequality-red.csv
1 "fixed acidity";"volatile acidity";"citric acid";"residual sugar";"chlorides";"free sulfur dioxide";"total sulfur dioxide";"density";"pH";"sulphates";"alcohol";"quality"
2 7.4;0.7;0;1.9;0.076;11;34;0.9978;3.51;0.56;9.4;5
3 7.8;0.88;0;2.6;0.098;25;67;0.9968;3.2;0.68;9.8;5
4 7.8;0.76;0.04;2.3;0.092;15;54;0.997;3.26;0.65;9.8;5
5 11.2;0.28;0.56;1.9;0.075;17;60;0.998;3.16;0.58;9.8;6
6 7.4;0.7;0;1.9;0.076;11;34;0.9978;3.51;0.56;9.4;5
7 7.4;0.66;0;1.8;0.075;13;40;0.9978;3.51;0.56;9.4;5
8 7.9;0.6;0.06;1.6;0.069;15;59;0.9964;3.3;0.46;9.4;5
9 7.3;0.65;0;1.2;0.065;15;21;0.9946;3.39;0.47;10;7
10 7.8;0.58;0.02;2;0.073;9;18;0.9968;3.36;0.57;9.5;7
11 7.5;0.5;0.36;6.1;0.071;17;102;0.9978;3.35;0.8;10.5;5
12 6.7;0.58;0.08;1.8;0.097;15;65;0.9959;3.28;0.54;9.2;5
13 7.5;0.5;0.36;6.1;0.071;17;102;0.9978;3.35;0.8;10.5;5
14 5.6;0.615;0;1.6;0.089;16;59;0.9943;3.58;0.52;9.9;5
15 7.8;0.61;0.29;1.6;0.114;9;29;0.9974;3.26;1.56;9.1;5
2. View with pretty format using column
# -s: specify delimiter, example here with semicolon
# -t: output as a tables
# < : redirect from stdin
$ column -s\; -t < winequality-red.csv| less -S -N
1 "fixed acidity" "volatile acidity" "citric acid" "residual sugar" "chlorides" "free sulfur dioxide" "total sulfur dioxide" "density" "pH" "sulphates" "alcohol" "quality"
2 7.4 0.7 0 1.9 0.076 11 34 0.9978 3.51 0.56 9.4 5
3 7.8 0.88 0 2.6 0.098 25 67 0.9968 3.2 0.68 9.8 5
4 7.8 0.76 0.04 2.3 0.092 15 54 0.997 3.26 0.65 9.8 5
5 11.2 0.28 0.56 1.9 0.075 17 60 0.998 3.16 0.58 9.8 6
6 7.4 0.7 0 1.9 0.076 11 34 0.9978 3.51 0.56 9.4 5
7 7.4 0.66 0 1.8 0.075 13 40 0.9978 3.51 0.56 9.4 5
8 7.9 0.6 0.06 1.6 0.069 15 59 0.9964 3.3 0.46 9.4 5
9 7.3 0.65 0 1.2 0.065 15 21 0.9946 3.39 0.47 10 7
10 7.8 0.58 0.02 2 0.073 9 18 0.9968 3.36 0.57 9.5 7
11 7.5 0.5 0.36 6.1 0.071 17 102 0.9978 3.35 0.8 10.5 5
12 6.7 0.58 0.08 1.8 0.097 15 65 0.9959 3.28 0.54 9.2 5
13 7.5 0.5 0.36 6.1 0.071 17 102 0.9978 3.35 0.8 10.5 5
14 5.6 0.615 0 1.6 0.089 16 59 0.9943 3.58 0.52 9.9 5
15 7.8 0.61 0.29 1.6 0.114 9 29 0.9974 3.26 1.56 9.1 5
3. Navigate directly to a specific pattern:
# +/: search for a pattern, e.g here with a timestamp
less +/03:00:00 sensor.xml
4. Search for a pattern:
# /: search for a pattern, e.g here with a timestamp
less /03:00:00 sensor.xml
# ?: search for a pattern in reverse
less ?03:00:00 sensor.xml
5. Monitor a growing log file:
less +F /var/log/syslog
less is a simple yet powerful tool to explore, search, and navigate large or complex filescolumn, grep, awk, sed, etc. to get the most out of your data-N, -S, +F, /, ?, make it especially effective for data exploration