Traps

Accustomed awk users should take special note of the following:

Semicolons are required after all simple statements in perl

(except at the end of a block). Newline is not a statement delimiter.
Curly brackets are required on ifs and whiles.
Variables begin with $ or @ in perl.
Arrays index from 0 unless you set $[. Likewise string positions in

substr() and index().
You have to decide whether your array has numeric or string indices.
Associative array values do not spring into existence upon mere

reference.
You have to decide whether you want to use string or numeric

comparisons.
Reading an input line does not split it for you. You get to split it

yourself to an array. And the split

operator has different arguments.

The current input line is normally in $_, not $0. It generally does

not have the newline stripped. ($0 is the name of the program executed.)
$<digit> does not refer to fields— it refers to substrings

matched by the last match pattern.
The print statement does not add field and record separators

unless you set $, and $\.
You must open your files before you print to them.
The range operator is ‘‘. .’’, not comma. (The comma operator works

as in C.)
The match operator is ‘‘=˜’’, not ‘‘˜’’. (‘‘˜’’ is the one’s

complement operator, as in C.)
The exponentiation operator is ‘‘**’’, not ‘‘ˆ’’. (‘‘ˆ’’ is the

XOR operator, as in C.)
The concatenation operator is ‘‘.’’, not the null string. (Using the

null string would render ‘‘/pat/ /pat/’’ unparsable, since the third slash would be interpreted as a division operator— the tokener is in fact slightly context sensitive for operators like /, ?, and <. And in fact, . itself can be the beginning of a number.)
Next, exit and continue work differently.
The following variables work differently

Awk Perl

ARGC $#ARGV

ARGV[0] $0

FILENAME $ARGV

FNR $. − something

FS (whatever you like)

NF $#Fld, or some such

NR $.

OFMT $#

OFS $,

ORS $\

RLENGTH length($&)

RS $/

RSTART length($`)

SUBSEP $;

Cerebral C programmers should take note of the following:

Curly brackets are required on ifs and whiles.
You should use ‘‘elsif’’ rather than ‘‘else if’’
Break and continue become last and next, respectively.
There’s no switch statement.
Variables begin with $ or @ in perl.
Printf does not implement *.
Comments begin with #, not /*.
You can’t take the address of anything.
ARGV must be capitalized.
The ‘‘system’’ calls link, unlink, rename, etc. return nonzero for

success, not 0.
Signal handlers deal with signal names, not numbers.

Seasoned sed programmers should take note of the following:

Backreferences in substitutions use $ rather than \.
The pattern matching metacharacters (, ), and  do not have

backslashes in front.
The range operator is . . rather than comma.

Sharp shell programmers should take note of the following:

The backtick operator does variable interpretation without regard to

the presence of single quotes in the command.
The backtick operator does no translation of the return value,

unlike csh.
Shells (especially csh) do several levels of substitution on each

command line. Perl does substitution only in certain constructs such as double quotes, backticks, angle brackets and search patterns.
Shells interpret scripts a little bit at a time. Perl compiles the

whole program before executing it.
The arguments are available via @ARGV, not $1, $2, etc.
The environment is not automatically made available as variables.