intro.awk

gistfile1.txt

# Big ideas
#
# - 2 types of shell tools
#   - Compute (ls, rm, find, grep, vim ..)
#   - Format  (sort, tail, cut, uniq, sed, ..) 
#   - awk is the ultimate formatting tool

# - a complete prog lang for text processing
#   - handle state on the cmd line
#   - 2 major datatypes

# - avoids pitfalls of other tools
#   - Python's ease, sed's power
#   - Good number support

# - Gotchas
#   - 1 based indexing
#   - no local variabels .__.



# Patterns and actions
# { print }
# /^a.*/ { print } 
# BEGIN { print "Beginning" } { print } END { print "End"; }
# BEGIN { print "Hello World!" }

# Variables and common sense
# { print $2 }
# { print $0 } # cat
# { print NR, $0 } # line number
# NR == 2 { print "Only", NR ",", $0 }
# { print NF, $0 } # number of fields
# { print length }
# {  # reverse each line
#    for (i = NF; i > 0; i--) { 
#        printf $i" ";
#    }
#    print "";
# }

# Print empty for empty lines
# length > 0 { print }
# /^$/ { print "empty" }

# Math
# /[0-9.]/ {
#     sum = 0;
#     for (i = 1; i <= length; i++) {
#        sum += $i # += is a numeric operation
#     }
#     print "sum:", sum
# }

# Shell like interface
# BEGIN {
#     cmd="ls ./"
#     while(cmd | getline line)
#         print line
# }

# Print the environment
# BEGIN {
#     printArray(SYMTAB, 1)
# }

# function printArray(arr,   level, i) {
#     if (!isarray(arr)) {
#         return;
#     }

#     for (i in arr) {
#         printf getIndent(level) i
#         if (isarray(arr[i]))
#             printf ":\n"
#         else
#             printf "\n"
#         printArray(arr[i], level + 1);
#     }
# }

# function getIndent(num,    indent, i) {
#     for (i = 1; i < num; i++) {
#         indent = (indent "\t");
#     }
#     return indent
# }

#:nnoremap -x :silent !gawk -f intro.awk < input.txt > output.txt<CR>