Tips for Shell
There will be some case-based tips for Shell.
1. Replace the sequence space with newline
Input example
a b c d
Output example
a
b
c
d
Summary
sed is the best solution.
Solution
sed -r -e 's/[[:space:]]/\n/g'
2. Sort the unordered word list (with duplication) by frequency
Summary
It is very useful when counting word frequency.
Solution
sort | uniq -c | sort -rn
3. Awk print line without first column
Summary
This command actually clear the first column from the file.
Solution
awk '{$1=""; print $0}'
4. Show the longest line in the file
Summary
Taking advantage of the const length in awk
Solution
awk '{print $0" "length}' | sort -k2 -nr | head -1
5. Ignore line that match some pattern
Summary and Solution
Using
grep -v
6. Batchly replace namespace
Summary
Using for to loop over the file and sed to perform the replacement.
Solution
for f in `find ./src -type f`; do sed -i 's/oldnamespace/newnamespace' $f; done
7. Generate 02, …, 24 sequence
Summary
Perl can be a better solution.
Solution
perl -e 'for{$i=2;$i<=24;$i++}{printf("%02d\n", $i)}'
8. Command line calculator
Awk Solution
awk '{print 1/10}'
and additional enter is needed
Perl Solution
More flexiable (with formatting).
perl -e 'printf("%f\n", 1./10);'