Strange shell behaviour -


here simple bash script:

a="asd" b="qf" echo "$a.$b" echo "$a_$b"

it's output is:

asd.qf qf

why second line not "asd_qf" "qf"?

because haven't defined variable named a_. second printout work, use:

echo "${a}_$b"

Comments

Post a Comment

Popular posts from this blog

JQuery Autocomplete without using label, value, id -

is possible have jquery autocomplete work without using conventional id,label,value? for instance, not wish use: [ { "id": "botaurus stellaris", "label": "great bittern", "value": "great bittern" }, { "id": "asio flammeus", "label": "short-eared owl", "value": "short-eared owl" }] but rather: [ { "my_id": "botaurus stellaris", "first_name": "great bittern", "last_name": "great bittern" }, { "my_id": "asio flammeus", "first_name": "short-eared owl", "last_name": "short-eared owl" }] so like, jquery autocomplete takes id,value,label , can make take my_id, first_name, last_name , make jquery autocomplete treat same id,label,value ? this might useful, when don't wish modify data's keys coming datasource, display on jquery autocomplete. ...
Read more

algorithm - Bellman-Ford: all shortest paths -

i've implemented bellman-ford find distance of shortest path when edges have negative weights/distances. i've not been able return shortest paths (when there ties shortest). managed shortest paths (between given pair of nodes) dijkstra. possible bellman-ford? (just want know if i'm wasting time trying) if alter second step of bellman-ford algorithm little bit can achieve similar: for 1 size(vertices)-1: each edge uv in edges: // uv edge u v u := uv.source v := uv.destination if u.distance + uv.weight < v.distance: v.distance := u.distance + uv.weight v.predecessor[] := u else if u.distance + uv.weight == v.distance: if u not in v.predecessor: v.predecessor += u where v.predecessor list of vertices. if new distance of v equals path isn't included yet include new predecessor. in order print shortest paths use like procedure printpaths(vertex current, vertex start, list used, string path): if current == start: print start.id + " -> " + path else...
Read more

c++ - Accessing inactive union member and undefined behavior? -

i under impression accessing union member other last 1 set ub, can't seem find solid reference (other answers claiming it's ub without support standard). so, undefined behavior? the confusion c explicitly permits type-punning through union, whereas c++ ( c++11 ) has no such permission. c11 6.5.2.3 structure , union members 95) if member used read contents of union object not same member last used store value in object, appropriate part of object representation of value reinterpreted object representation in new type described in 6.2.6 (a process called ‘‘type punning’’). might trap representation. the situation c++: c++11 9.5 unions [class.union] in union, @ 1 of non-static data members can active @ time, is, value of @ 1 of non-static data members can stored in union @ time. c++ later has language permitting use of unions containing struct s common initial sequences; doesn't permit type-punning. to determine whether union type-punning is allowe...
Read more