lsearch(3tcl)

💖 lsearch — the Tcl Built-In Commands glow-up 💖

okay bestie, pull up a chair, because lsearch is one of those commands that looks tiny in the synopsis and then hits you with like 20 options. it's giving "quiet girl in class who's secretly a genius". and yes, this is the Tcl Built-In Commands manual, page lsearch(3tcl), and we're gonna get through all of it together, no skipping, periodt. 🎀

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✨ NAME ✨

lsearch — See if a list contains a particular element (spoiler: it does, and it will tell you exactly where)

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🌸 SYNOPSIS 🌸

lsearch ?options? list pattern

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🦋 DESCRIPTION 🦋

so the whole vibe: this command searches the elements of list to see if one of them matches pattern. if so, the command returns the index of the first matching element — unless you passed -all or -inline, in which case it does something fancier. if not, it returns -1, or (if -all or -inline are specified) the empty string. it's giving "I'll find them, and if they're not there I'll just Say Nothing."

the option arguments tell lsearch how the elements of the list are to be matched against pattern, and each one must have one of the values below. let's go. 👑

💅 MATCHING STYLE OPTIONS

if all matching style options are omitted, the default matching style is -glob. and if more than one matching style is specified? the last matching style given takes precedence. the last one wins, always, like whoever speaks last at the function. 🙈

• -exact — Pattern is a literal string that is compared for exact equality against each list element.
• -glob — Pattern is a glob-style pattern which is matched against each list element using the same rules as the string match command.
• -regexp — Pattern is treated as a regular expression and matched against each list element using the rules described in the re_syntax reference page.
• -sorted — The list elements are in sorted order. If this option is specified, lsearch will use a more efficient searching algorithm to search list. If no other options are specified, list is assumed to be sorted in increasing order, and to contain ASCII strings. This option is mutually exclusive with -glob and -regexp, and is treated exactly like -exact when either -all or -not are specified.

ok so -sorted is the "I already did the work, don't @ me" option. it's literally a whole shortcut and it's not compatible with -glob or -regexp, so don't try it. mutual exclusivity means mutual exclusivity. 🚫

🌈 GENERAL MODIFIER OPTIONS

these options may be given with all matching styles. all of them. every single one. they're the little accessories that go with any outfit. 🫶

• -all — Changes the result to be the list of all matching indices (or all matching values if -inline is specified as well.) If indices are returned, the indices will be in ascending numeric order. If values are returned, the order of the values will be the order of those values within the input list.
• -inline — The matching value is returned instead of its index (or an empty string if no value matches.) If -all is also specified, then the result of the command is the list of all values that matched.
• -not — This negates the sense of the match, returning the index of the first non-matching value in the list.
• -start index — The list is searched starting at position index. The interpretation of the index value is the same as for the command string index, supporting simple index arithmetic and indices relative to the end of the list.

🍓 CONTENTS DESCRIPTION OPTIONS

these options describe how to interpret the items in the list being searched. they are only meaningful when used with the -exact and -sorted options. if more than one is specified, the last one takes precedence. the default is -ascii.

• -ascii — The list elements are to be examined as Tcl strings (i.e. sequences of Unicode code points; the name is for backward-compatibility reasons.)
• -dictionary — The list elements are to be compared using dictionary-style comparisons (see lsort for a fuller description). Note that this only makes a meaningful difference from the -ascii option when the -sorted option is given, because values are only dictionary-equal when exactly equal.
• -integer — The list elements are to be compared as integers.
• -nocase — Causes comparisons to be handled in a case-insensitive manner. Has no effect if combined with the -dictionary, -integer, or -real options.
• -real — The list elements are to be compared as floating-point values.

ngl the -nocase one has beef with -dictionary, -integer and -real. it literally does nothing when you pair them up. it's giving "I'm not coming to the group project". 💀

🧚 SORTED LIST OPTIONS

these options (only meaningful with the -sorted option) specify how the list is sorted. if more than one is given, the last one takes precedence. the default option is -increasing.

• -decreasing — The list elements are sorted in decreasing order. This option is only meaningful when used with -sorted.
• -increasing — The list elements are sorted in increasing order. This option is only meaningful when used with -sorted.
• -bisect — Inexact search when the list elements are in sorted order. For an increasing list the last index where the element is less than or equal to the pattern is returned. For a decreasing list the last index where the element is greater than or equal to the pattern is returned. If the pattern is before the first element or the list is empty, -1 is returned. This option implies -sorted and cannot be used with either -all or -not.

-bisect is the main character here lowkey. it implies -sorted on its own (iconic, self-sufficient) but it cannot be used with -all or -not. and if the pattern is before the first element or the list is empty, you get -1. that's the whole deal, no cap.

⭐ NESTED LIST OPTIONS

these options are used to search lists of lists. they may be used with any other options. lists inside lists inside vibes. 🪆

• -stride strideLength — If this option is specified, the list is treated as consisting of groups of strideLength elements and the groups are searched by either their first element or, if the -index option is used, by the element within each group given by the first index passed to -index (which is then ignored by -index). The resulting index always points to the first element in a group.
• -index indexList — This option is designed for use when searching within nested lists. The indexList argument gives a path of indices (much as might be used with the lindex or lset commands) within each element to allow the location of the term being matched against.
• -subindices — If this option is given, the index result from this command (or every index result when -all is also specified) will be a complete path (suitable for use with lindex or lset) within the overall list to the term found. This option has no effect unless the -index is also specified, and is just a convenience short-cut.

and the -stride rules, which you need to know:

The list length must be an integer multiple of strideLength, which in turn must be at least 1. A strideLength of 1 is the default and indicates no grouping.

fr fr — if your list length doesn't divide evenly, that's a problem, and strideLength has to be 1 or more. default is 1, which just means "no grouping, we're not doing the group thing". 💖

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🔥 EXAMPLES 🔥

Basic searching

lsearch {a b c d e} c
      → 2
lsearch -all {a b c a b c} c
      → 2 5

Using lsearch to filter lists

lsearch -inline {a20 b35 c47} b*
      → b35
lsearch -inline -not {a20 b35 c47} b*
      → a20
lsearch -all -inline -not {a20 b35 c47} b*
      → a20 c47
lsearch -all -not {a20 b35 c47} b*
      → 0 2

This can even do a “set-like” removal operation

lsearch -all -inline -not -exact {a b c a d e a f g a} a
      → b c d e f g

Searching may start part-way through the list

lsearch -start 3 {a b c a b c} c
      → 5

It is also possible to search inside elements

lsearch -index 1 -all -inline {{abc abc} {abc bcd} {abc cde}} *bc*
      → {abc abc} {abc bcd}

The same thing for a flattened list

lsearch -stride 2 -index 1 -all -inline {abc abc abc bcd abc cde} *bc*
      → abc abc abc bcd

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💜 SEE ALSO 💜

foreach(3tcl), list(3tcl), lappend(3tcl), lassign(3tcl), ledit(3tcl), lindex(3tcl), linsert(3tcl), llength(3tcl), lmap(3tcl), lpop(3tcl), lrange(3tcl), lremove(3tcl), lrepeat(3tcl), lreplace(3tcl), lreverse(3tcl), lseq(3tcl), lset(3tcl), lsort(3tcl), string(3tcl)

(the whole list family showed up to the group chat, as they should 💅)

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👑 KEYWORDS 👑

binary search, linear search, list, match, pattern, regular expression, search, string

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and that's the page, bestie. every flag, every default, every index, every -1, all of it — untouched, just with better energy. go search something. 🦋

Tcl 8.6 — lsearch(3tcl), brought to you by Tcl 8.6 (the footer said so, and I would never lie to you). mwah. 💖✨🎀