Chapter 10 Advanced File Processing

Regular Expressions A compact notation for representing patterns in strings Used by many common Linux utilities such as: – less/more – ed – vi – emacs – egrep – grep – fgrep – awk – sed – lex – perl – python

Table 10.1 Regular Expression Operators

Table 10.1 More Regular Expression Operators

Regular Expression Examples cat|dog matches "cat" or "dog“..at matches any three-character string ending with "at", including "hat", "cat", and "bat". [hc]at matches "hat" and "cat". [^b]atmatches all strings matched by.at except "bat". ^[hc]at matches "hat" and "cat", but only at the beginning of the string or line. [hc]at$matches "hat" and "cat", but only at the end of the string or line.

Regular Expression Examples (0|1)+ 1+0* a*ba*ba* [A-Za-z][A-Za-z0-9]* (yaba|daba)+doo

Table 10.2 Examples of Regular Expressions for vi and Their Meaning

Table 10.3 Some Commonly Used vi Commands Illustrating the Use of Regular Expressions

File Compression compress uncompress gzip gunzip gzexe zcat zmore uuencode uudecode

Figure 10.1 The process of uuencoding and uudecoding

The Sort Utility Sorts lines of ASCII text Options for: – Ascending/descending order – Case folding – Ignoring leading whitespace – Alpha/numeric – Multiple keys

sort - sort lines of text files Syntax sort [OPTION]... [FILE]... Options -b, --ignore-leading-blanks ignore leading blanks -d, --dictionary-order consider only blanks and alphanumeric characters -f, --ignore-case fold lower case to upper case characters -i, --ignore-nonprinting consider only printable characters -n, --numeric-sort compare according to string numerical value -r, --reverse reverse the result of comparisons Other options: -k, --key=POS1[,POS2] start a key at POS1, end it at POS2 (origin 1) -t, --field-separator=SEP use SEP instead of non-blank to blank transition

Sort examples File donors.dat Bay Ching China Jack Arta Indonesia Cruella Lumper Malaysia sort donors.dat Bay Ching China Cruella Lumper Malaysia Jack Arta Indonesia

Sort Example – by last name sort +1 donors.dat Jack Arta Indonesia Bay Ching China Cruella Lumper Malaysia

Sort Example – by donation amount sort +2 donors.dat Jack Arta Indonesia Bay Ching China Cruella Lumper Malaysia sort +2 -n donors.dat Jack Arta Indonesia Bay Ching China Cruella Lumper Malaysia sort +2 -n -r donors.dat Cruella Lumper Malaysia Bay Ching China Jack Arta Indonesia

Locating Files find whereis which

Find command Syntax Find directory-list expression Searches directory-list for files that match conditions in expression Can find files by name, owner, permission, size, age, links

Find Command Examples find ~ -name *.gif -print find / -name socket.h -print find / -size c -print find ~ -newer filetocompare

Searching File Contents grep egrep fgrep

Grep – Get Regular Expression & Print Syntax grep [options] pattern [file-list] Searches files in file-list, prints lines which match the given pattern Options to fold case, print line #’s, filenames, non- matching lines fgrep – faster but dumb egrep – slower but more powerful

Command History A list of the recently used commands is maintained and controlled by the variables: – HISTSIZE – HISTFILE – HISTFILESIZE

Table 10.4 Commonly Used Event Designators for History Expansion

Table 10.5 Commonly Used Event Designators for History Expansion

Table 10.6 Commonly Used Modifiers for History Expansion