UNIX for Dummies Questions & Answers

#!/usr/bin/env bash

# @(#) s1	Demonstrate keeping lines in shell memory, variables.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C specimen tail

# Stage new sample data file.
cp data0 data1

FILE=${1-data1}

pl " Input data file $FILE:"
specimen 3 $FILE

pl " Results:"
v1=$( tail -3 $FILE )
rm $FILE
echo "$v1" > $FILE
specimen 3 $FILE

exit 0

$ ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny, workstation) 
bash GNU bash 3.2.39
specimen (local) 1.17
tail (GNU coreutils) 6.10

-----
 Input data file data1:
Edges: 3:0:3 of 26 lines in file "data1"
Four score and seven years ago our fathers brought forth on this
continent a new nation, conceived in Liberty, and dedicated to
the proposition that all men are created equal.
   ---
under God, shall have a new birth of freedom--and that
government: of the people, by the people, for the people, shall
not perish from the earth.

-----
 Results:
Whole: 3:0:3 of 3 lines in file "data1"
under God, shall have a new birth of freedom--and that
government: of the people, by the people, for the people, shall
not perish from the earth.

n=50000; start=$(( $(wc -l file | cut -d' ' -f1) - $n + 1 )); sed -ni ${start},\$p file

sed -e :a -e '$q;N;50001,$D;ba'

-i[SUFFIX], --in-place[=SUFFIX]

              edit files in place (makes backup if SUFFIX supplied)

ex -sc '$-49999,$d | x' file

-i extension
             Edit files in-place, saving backups with the specified extension.
             If a zero-length extension is given, no backup will be saved.  It
             is not recommended to give a zero-length extension when in-place
             editing files, as you risk corruption or partial content in situ-
             ations where disk space is exhausted, etc.